This addresses part of #197

Use a RecyclerView for the Contact List

This is the first RecyclerView in the project. I am using a SortedList to keep the contacts sorted by latest activity.

Also, I removed the icon footer and moved the icon into ActionBar. I did the same with the long-press contact deletion action which eventually will move to the new contact details activity.

Several icons have been replaced by vector drawables and all the views are now defined in XML.

See merge request !38

When you receive a message from a contact,
it will be moved to the top of the list with a nice animation.
Also with this commit, not the entire data set is invalidated each time data changes,
but only the parts of the data that really require an update.

Furthermore, the ContactListItemComparator that is not needed anymore is
removed.

Inject dbExecutor as ExecutorService

Closes #188, despite the branch name. :0)

See merge request !33

Small Improvements for Crash Handling Activities

This relates to #7 and closes #193

See merge request !37

Fix off-by-one error in key rotation

Fixes #190.

See merge request !32

Put labels below transport icons

This prevents the labels from wrapping on small screens. Fixes #191.

See merge request !34

Update dashboard icons when resuming activity.

Fixes #186. 

The issue is that DashboardActivity doesn't receive events while it's paused. This appears to be device-dependent because it depends on the relative speed of resuming the activity vs delivering the event. If the activity resumes quickly enough, it will register its event listener and catch the event. If not, it won't update its icons until it's recreated, e.g. by rotating the screen.

See merge request !31

Switch KDF from SHA-256 to Blake2. #169

The BTP spec calls for Blake2s, but there's no Java implementation available. I suggest we go with Blake2b for now. If it turns out to be a performance bottleneck on 32-bit platforms we can consider implementing Blake2s and merging it upstream.

This depends on !13.

See merge request !21

Stream encryption for BTP version 2. #111

This patch implements the stream header from the BTPv2 spec (https://code.briarproject.org/akwizgran/briar/wikis/BTP).

This merge request depends on !13.

See merge request !18

Longer explanatory text for Tor mobile data setting



See merge request !29

Layout tweaks for ConversationActivity.

Centre the progress wheel and empty list message, hide the empty list message until the list has loaded.

See merge request !26

Replace bluetooth diagram PNG image with vector XML file.

I decided to not use several raster graphics, but use an XML file instead, so the android gradle plugin creates the raster files itself at build-time. I hope that this resolves the problem you saw on that device of yours.

See merge request !30

Show which transports are currently available

Show all transports on the dashboard and indicate which transports are currently available.
The icons have been chosen from the official material icons and might be
replaced later with icons that better represent the given transport.

Please note that I used vector drawables which will be automatically
converted at build time to raster graphics.

See merge request !28

Closes #179