The text of the startup failure notification is unhelpful due to lack of
space. Touching the notification now launches an activity that gives details
of the problem and what can be done about it.

Closes #38

This breaks backward compatibility for the wire protocol and messages
stored in the database. The database schema version has been
incremented.

Android L requires executables to be compiled with PIE support, so we'll
have to ship two Tor binaries.

Of course, not all devices support Bluetooth...

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

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

Some Android devices require a lock to be held while using multicast, to
disable the packet filter that normally filters out multicast packets.