Forum Sharing Client Backend

This MR replaces the old `ForumSharingManagerImpl` with a new one
which is based on state machines and the `ProtocolEngine`.

There is a `SharerEngine` and a `InviteeEngine` that take care of state
transitions, messages, events and trigger actions to be carried out by
the `ForumSharingManagerImpl`. This is all very similar to the
Introduction Client.

The general sharing paradigm has been changed from sharing as a state to
sharing as an action. Now the UI can allow users to invite contacts to
forums. The contacts can accept or decline the invitation. Also, the
Forum Sharing Manager is notified when users leave a forum.

Please note that you will need the UI to actually test this. It is coming up soon in another MR.

Closes #322

See merge request !170

Store a fixed number of recent IP addresses, padded with fakes

Closes #302

See merge request !159

Includes parallel improvements to Bluetooth key exchange UI.

Use control port to create and set up Tor hidden service

Closes #149

See merge request !160

Remember the selected fragment from the NavDrawer

and stay in it when configuration changes

Closes #370

See merge request !176

Do not allow session ID reuse and clean up sessions for introducee

It was possible that a malicious introducer sends new request with the
same session ID that was used previously and thus causing introducees to
have multiple states for the same session ID.
This commits prevents that from happening and adds an integration test
for that scenario.

Also if an introducee removes an introducer, all past session states
will be deleted from the database. For this, a test was added as well.

Closes #371
Closes #372

See merge request !179

It was possible that a malicious introducer sends new request with the
same session ID that was used previously and thus causing introducees to
have multiple states for the same session ID.
This commits prevents that from happening and adds an integration test
for that scenario.

Also if an introducee removes an introducer, all past session states
will be deleted from the database. For this, a test was added as well.

Closes #371
Closes #372

This commit replaces the old ForumSharingManagerImpl with a new one
which is based on state machines and the ProtocolEngine.

There is a SharerEngine and a InviteeEngine that take care of state
transitions, messages, events and trigger actions to be carried out by
the ForumSharingManagerImpl. This is all very similar to the
Introduction Client.

The general sharing paradigm has been changed from sharing as a state to
sharing as an action. Now the UI can allow users to invite contacts to
forums. The contacts can accept or decline the invitiation. Also, the
Forum Sharing Manger is notified when users leave a forum.

Closes #322

and stay in it when configuration changes

Closes #370

Restore opaque background to progress wheels

Closes #340

See merge request !174

Move forum removal action from long press menu to action bar

This is part of the UI changes for #305 

See merge request !164

part of UI changes for #305

Set ongoing notification to minimum priority

Setting the priority of the ongoing notification to PRIORITY_MIN prevents it from being shown in the status bar on Android 4.1 and later. The service still runs in the foreground.

Thanks to @str4d for finding the solution. Closes #154.

See merge request !169

Prepare for new Forum Sharing Client

Methods for creating, adding and removing forums have been moved to the
`ForumManager`. In order to still handle removing forums properly, a
`RemoveForumHook` has been introduced.

Methods for sharing forums with all current and future contacts have
been removed along with the localGroup where this information was saved.

The `ShareForumActivity` now has the proper label.

The `SessionId` and the `ProtocolEngine` have been moved to the
`clients` package.

This addresses part of #322 and part of what has been discussed in #320.

See merge request !156

Methods for creating, adding and removing forums have been moved to the
`ForumManager`. In order to still handle removing forums properly, a
`RemoveForumHook` has been introduced.

Methods for sharing forums with all current and future contacts have
been removed along with the localGroup where this information was saved.

The `ShareForumActivity` now has the proper label.

The `SessionId` and the `ProtocolEngine` have been moved to the
`clients` package.

This addresses part of #322 and part of what has been discussed in #320.

Hold a wake lock while Tor is connected to the internet

This is a partial fix for #314. As noted on that ticket, if a Tor connection is lost for any reason other than the device sleeping, the plugin won't try to replace the lost connection. I'm leaving the ticket open until that more general issue is solved.

The Tor plugin uses several variables to keep track of its connectivity status. This patch refactors those variables into an inner class to improve readability and ensure they're accessed atomically. However, it's still possible for the plugin's state to become inconsistent with the state of the Tor process. For example, calls to updateConnectionStatus() may run concurrently on the IO executor, so their calls to enableNetwork() may be interleaved. As usual, locking would solve this problem but create the potential for deadlock, so I won't try to solve it in this patch.

See merge request !168

Fix name of Tor mobile data setting

Closes #316.

See merge request !167

Reinitialise viewfinder when camera view is shown

Thanks to @str4d for finding the cause of the bug. Closes #331.

See merge request !165

Use Android executor for background API calls

Some Android API calls need to be made from a thread with a message queue, but to keep the UI responsive they shouldn't be made from the UI thread.

This patch gives AndroidExecutor a captive thread with a message queue to execute tasks, and converts various background tasks from creating their own threads to using AndroidExecutor and IoExecutor.

This allows us to upgrade the support library to 23.2.1. Fixes #332.

See merge request !161

Add Snackbar and Toolbar Button to Forum List

This MR is a small change that replaces the custom UI elements in
the forum list with a Snackbar and a Toolbar menu.

It also fixes a background color that was still present with fragment from the NavDrawer.

Before:

![before](/uploads/6dcc545827c035dcffcdf7863893753e/before.png)

After:

![after](/uploads/427de01d8bec779ee81e6ebded3fcd2b/after.png)

It addresses one part (2b) of #305 and is part of #121.


See merge request !163

This commit is a small change that replaces the custom UI elements in
the forum list with a Snackbar and an Toolbar menu.

Addresses one part (2b) of #305