Add TSDatabaseDidUpdateNotification to the database.
Use string const for database update notifications.
Get rid of bug leading to crash when no messages are present in the db.
Remove duplicated UIAppearance proxy customisations.
Use NSData category for base64 encoding.

- Removes a compiler warning
Merge branch 'master' of https://github.com/ursachec/TextSecure-iOS into ursachec-master