Send from compose screen functions properly

Implemented a fix for the bug where messages sent from the compose
screen weren't added to the database if there wasn't an existing
conversation with the intended recipient.
Hypothetically, notifications should work pre-4.1

Rewrote displayNotification() to work in pre-Jellybean environments.
Can't test it yet because I don't have access to a pre-Jellybean device,
but it should work.