Add SMS Middleware layer.

Change-Id: I4fff0c584f8fce9c5f2f4fe86a82fe6480c307c7
CallTracker: Add back-off and retry toggle to getCurrentCalls

Add a system property to handle cases where the modem
reacts slowly and does not update CURRENT_CALLS to include calls which
are dialing. A delay is introduced to avoid spamming the modem and then
GetCurrentCalls is called again in order to avoid the calltracker from
marking the call as ended when it is still active.

Tested and LS970 and E970 (Sprint and ATT LG Optimus G).

Change-Id: I7d3aac00b811bceb2909adf239492962a737de4a