Material design settings - alternative

Closes #206.

Alternative to !77 that does not rely on an additional external library. The two alternatives should be compared for backwards-compatibility specifically regarding the ringtone selector.

Includes code from https://github.com/consp1racy/android-support-preference
License: Apache License v2.0

See merge request !78

Message queues. #266

A message queue is a group shared by two devices that delivers messages from each device to the other in order. The first 64 bits of the message body contain a sequence number that's incremented for each message sent in a given direction. The incoming and outgoing sequence numbers and information about any messages received out of order and waiting to be delivered are stored in the group metadata.

See merge request !121

Includes code from https://github.com/consp1racy/android-support-preference
License: Apache License v2.0

Fix race condition when closing redundant Bluetooth sockets

The Bluetooth invitation code has a race condition: if Alice and Bob connect to each other at roughly the same time, they each consider their outgoing socket to be redundant and close it, resulting in both sockets being closed. This can be triggered pretty reliably by using two phones of the same model and pressing 'Continue' at the same time on both phones.

When more than one invitation socket is opened, Alice should pick which one to use and Bob should use whichever one Alice picks, which Bob can detect by trying to read from both sockets.

Hopefully the Bluetooth invitation code will be retired when #117 is merged, but I'm putting this up for review in case we need to keep Bluetooth as a fallback method.

See merge request !120

Delete all app data when deleting account. #263

When deleting the user's account, delete everything in the app's persistent storage directory except the libs directory, which is populated with native libs when the app is installed.

Fixes #263.

See merge request !119

Use client helper in existing clients

Use the new ClientHelper to reduce boilerplate in existing clients. Add a BdfMessageValidator superclass for clients that format their messages as BDF lists and their metadata as BDF dictionaries (which all existing clients do).

See merge request !115

When more than one invitation socket is opened, Alice should pick which one to use and Bob should use whichever one Alice picks. This fixes a race condition where each party picked a different socket and closed the other.

BDF improvements

* Change the semantics of the BdfList/Dictionary methods with default values so they return the default value if the value is missing, or throw an exception if it the value's present but has the wrong type - this is more useful for validators, which have to deal with optional values without accepting values of the wrong type
* Reuse BdfReader/Writer for MetadataParser/Encoder so we don't have two implementations of BDF


See merge request !117

Helper class to reduce client boilerplate

* Renamed BdfReader methods for consistency with BdfList/BdfDictionary
* Added readList() and readDictionary() methods to BdfReader
* Added ClientHelper to reduce boilerplate when converting messages and metadata to and from BDF
* Moved PrivateGroupFactory to the same package as ClientHelper


See merge request !114

Unit tests for ValidationManagerImpl

Unit test for the validation manager. I also changed the way the validation manager loads unvalidated messages - instead of using a single DB task to load all unvalidated messages, it loads a list of message IDs and then loads each message in a separate task. This prevents the DatabaseExecutor from being blocked by a long-running task if there are lots of messages to validate.

See merge request !113