Don't crash if camera is reopened or surface is recreated

This branch fixes the crash is described in #720, which can be reproduced easily by scanning a QR code and failing to connect (for example, scan a screenshot of a QR code from a device that's no longer listening). When the camera view becomes visible again after trying to connect, its surfaceCreated() callback is called again with the same surface. An IllegalStateException added in !340 causes the crash.

Closes #720

See merge request !397

Make the feed pager respond to events, block notifications

This branch fixes a bug I found while working on #705: FeedPostPagerFragment doesn't start or stop the controller, so it doesn't load newly received posts or block notifications, unlike FeedFragment.

See merge request !398

Encode transport properties more compactly in QR codes

The [original BQP spec](https://code.briarproject.org/akwizgran/briar/wikis/BQP) described a compact encoding for transport properties, with the goal of making the QR code as small as possible. At some point during the implementation, I asked @str4d to use TransportIds and TransportProperties instead, as described in the [current spec](https://code.briarproject.org/akwizgran/briar-spec/blob/master/protocols/BQP.md). That was a mistake.

Using the original format reduces the payload from 60 to 34 bytes (43% smaller) for Bluetooth only, and from 96 to 49 bytes (49% smaller) for Bluetooth and LAN. This makes it easier to scan codes from low-resolution screens using fixed-focus and/or low-resolution cameras. Using this branch I can exchange codes between the Sony Xperia Tipo (320x480 screen, fixed focus, 640x480 preview size) and the Huawei Ascend Y300 (480x800 screen, infinity focus, 1280x720 preview size).

This also removes an obstacle to implementing #558, as TransportIds are no longer included in QR codes.

Closes #346.

See merge request !394

Private group invitation protocol

This branch implements the private group invitation protocol. The implementation is something of an experiment with a new way of writing client protocols.

We start with a role enum that lists the roles in the protocol, and a state enum for each role, which lists the states in the role's state machine. Then there's a session class, parameterised by the state class and therefore by the role, which represents the session information held by that role. Then there's an engine interface, parameterised by the session class and therefore by the role, which encapsulates the protocol logic for the role. Most of this stuff can be created pretty mechanically from the state machine diagrams.

The engine interface has a method for each type of message and each local action. I started out with one method for all messages and another for all local actions, but that turned out to be a bad design - the information about what kind of message was being handled was lost when the message was passed to the engine, and had to be recovered using an instanceof ladder.

Each engine method takes a message or an action and a session, and returns an updated session. A transaction is passed in so the engine can send messages, attach events, and do any other work it needs to do (such as changing the visibility of groups, in the case of this protocol). This removes the need to run tasks outside the engine, so the protocol logic is better encapsulated inside the engine.

Parsing and encoding of messages and sessions is separated from protocol logic. MessageParser, MessageEncoder and the validator are the only classes that know how messages and their metadata are formatted, and likewise SessionParser and SessionEncoder are the only classes that know how sessions are formatted. The metadata keys are declared in a package-private interface.

It's common knowledge that I never make mistakes, so to keep things interesting I've hidden 114 deliberate mistakes in this code. See how many you can spot!

Needs tests before #709 is closed.

See merge request !382

Preliminaries for private group invitation protocol

As promised, here's the preliminary stuff for #709 as a separate MR.

See merge request !395

Use namespaced strings for client IDs

Closes #557

See merge request !393

Mark private messages read properly

Depends on !386.

This branch uses the same approach as forums to mark messages read, i.e. each message is marked read when it becomes visible, rather than marking all messages read in a batch when the activity finishes. This fixes two problems: messages not being marked read when isFinishing() is false, for example when leaving the activity via the home button, and a race condition between updating and loading the group count when leaving the activity, resulting in a stale unread message count in the contact list.

Closes #196.

See merge request !388

Broadcast GroupMessageAddedEvent for the UI to update when received

Closes #733

See merge request !390

Create GroupDissolvedEvent and react to it

This MR also makes the private group list react to incoming group invitations (once they are implemented).

![device-2016-11-07-155240](/uploads/84ed51cf72bf2c7c597a0fd68b5d868c/device-2016-11-07-155240.png)
![device-2016-11-07-155302](/uploads/446c98d70d674d0bcd79bfb7682dfed5/device-2016-11-07-155302.png)

Closes #736, #737

See merge request !392

Also react to incoming group invitations

Show Notifications for Group Messages

Closes #734

See merge request !391

Return to group after not inviting new members

This MR also closes the keyboard when returning from the message fragment.

Closes #735

See merge request !389

Fixed asynchronous Activity leaks in Fragments

If a Fragment has been detached its `getActivity()` method will return null, providing numerous crash possibilities within the app.

My approach to fixing this is to make Fragments use their own `runOnUiThreadUnlessDestroyed` method, which also checks if the Fragment has been detached before running the Runnable

Closes #714

See merge request !387

Also close keyboard when returning from message fragment

Use contact ID rather than messaging group ID to identify conversation

We originally used the private messaging group ID to identify the private conversation, but now that the conversation includes messages from multiple clients it's more appropriate to use the contact ID.

This refactoring isn't urgent - I've had the branch lying around for a while, but I'm putting it up for review because #734 will touch some of the same code.

See merge request !386

Allow messages to be deleted in delivery hook

Closes #643

See merge request !385

Add unit tests for KeyManagerImpl

This also creates a `TransportKeyManager` interface and a factory for that to be able to test things separately.

Closes #205

See merge request !380

interface and a factory for that.

Let only the creator invite new members to private groups

A little bug I noticed when reviewing the implementation of the invitation protocol.

See merge request !383

Remove new member announcement and add signature to join message



See merge request !384