Don't display sender in outgoing message details

Because we don't know it. Fixes WhisperSystems#711.
Don't show letter count inside a push group or when SMS mode is disabled
Merge pull request #805 from wickedshimmy/fix-sender-details

Don't display sender in outgoing message details
Merge pull request #795 from benalbrecht/nocount

Don't show letter count when SMS mode is disabled
Add option to disable screen security

See WhisperSystems/TextSecure#788
Merge pull request #794 from SamWhited/issue788

Add option to disable screen security
Update behavior for incoming SMS path.

1) On KitKat, unencrypted SMS messages are never stored in
   TextSecure unless it is set as the system-wide default.

2) On KitKat, if TextSecure is set as the system-wide default,
   provide an option to change the default to a different app.

3) Don't store the TextSecure challenge on KitKat+ devices.
Merge remote-tracking branch 'upstream/master'