Remove the Toast that always says 'Message Sent' and show graphical
indicators instead that show either:
* message is waiting to be sent
* message was sent (or requested)
* message was delivered

H2 was failing to load its driver class on OpenJDK 6 because the code was compiled for Java 7.

"synchLock" will become confusing when we have lots of objects with "sync" in the name.

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

Also reduced hash function to 256 bits because our target security level
is now 128 bits.