If the schema of the database is incompatible with the schema expected
by the code, the database throws a DbSchemaException. LifecycleManager
indicates the error to BriarService, which uses HomeScreenActivity to
show a notification and quit the app.

Note that some devices (I'm looking at you, Huawei U8110) misreport
connectivity by failing to set EXTRA_NO_CONNECTIVITY and returning true
from ConnectivityManager.getActiveNetworkInfo().isConnected() when
there's no connectivity.

The latest version of libevent (2.0.21-stable) works fine.

Fixes bug #7. The service is restarted after a crash even if
onStartCommand() returns START_NOT_STICKY, but after restarting the DB
key is not restored and so the app can't usefully proceed.

The distinction between inbox groups and other groups can be maintained
internally, there's no need to represent it on the wire.

This allows us to avoid instantiating the plugin on unsupported
architectures.

Private messages are now the same as group messages, but groups can be
private or public. When a contact is added, a private group is created
and designated as the inbox for exchanging private messages with the
contact.

This produces a saner user experience when devices have differing
clocks.

This allows quick access to any part of the app, including quitting (two
touches).

This makes the contact list behave how alpha testers expected: touching
a contact shows private messages exchanged with the contact.