Hopefully this gives users a better understanding of whether their
messages and contacts are accessible than "Briar is running" and "Quit".

This give a simple and usable interface; we can worry about collapsing
blocks of read messages later.

GroupActivity needs to receive a similar treatment.

All JVMs must support UTF-8 encoding.

This adds complexity but will save a lot of bandwidth, as most of the
strings and byte arrays we want to send are less than 128 bytes.

The extra complexity isn't exposed outside of the serial component.

Upgrade jnotify to 0.94 to support 64-bit

This upgrades to 0.94 and selects the correct native lib via ${os.arch}. The binaries are from the jnotify sourceforge download page, you can verify them. Also patched up build.xml to display stack trace when exceptions are thrown inside a test.

This avoids a possible problem where the app expires while it's running
and every activity shows the expiry warning, leaving the user with no
way to quit.

See
https://developer.android.com/guide/topics/ui/notifiers/notifications.html#NotificationResponse

This will allow any activity to show the expiry warning and password
prompt, and to start and stop BriarService.

SplashScreenActivity, SetupActivity, ExpiryActivity and PasswordActivity
are special cases.

We check for compatibility by specifying a schema version and minimum
schema version in the code, storing them in the DB, and checking whether
the DB is too old for the code or vice versa.

This may help with bug #27, but it doesn't solve it in all cases (eg the
contact's device restarting).

Dev task #52. Known but unverified identities are also supported, but
currently unused. These will be used in future for contacts who've been
introduced but not verified face to face.