1) Don't add a notification item to the notification bar if the thread the
message is for is active and visible.
2) Only sound the notification ringtone at 1/4th volume if the thread the
message is for is active and visible.
3) Auto-clear the notification in the notification bar when a thread becomes
visible from a screen-off situation.
4) Make notification updates asynchronous.
1) Refactor recipient class to support asynchronous loading operations.
2) Refactor recipient factory to simplify recipient access.
3) Consoliate everything into one recipient provider that is capable of
doing async lookups and intelligent caching.
