SMS message auto persisting for sending

1. Added auto persisting when sending SMS messages. This feature is
enabled by a system property to avoid breaking existing apps.
2. Removed SMSDispatcher.mRemainingMessages and added per message
sending part count for sending multipart messages.
3. Refactored code to handle message sent or failed. Fixed bug that in
some situation SendNextMsg is not sent for failures.

Change-Id: I3298b139e484f1238a5c04dcc39fa88398bba679