* Only show them as unread when they arrive out of order
* Mark all messages as read when sending a message

BdfList and BdfDictionary are no longer thread-safe, they require external locking. Metadata (which is the class that will be passed across API boundaries) is still thread-safe.

Addresses comments for !48.

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

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

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