Addresses comments for !48.

Use BLAKE2s to generate tags.
KDF arguments for key rotation.
Frame IV format.

SHA-256 is still used for password-based key derivation (will be replaced with Argon2) and Fortuna.

Implementation is based on the BLAKE2b implementation from BouncyCastle, and is
therefore licensed under the BouncyCastle license (which will make future
upstreaming of the code easier).

Removed methods that are no longer needed for Java 6, moved the remaining method into the utils directory.

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.