Add OBEX object count support to Bluetooth.

To support Android Beam receiving information about
the number of files in a OPP transfer, add the Count
OBEX header. Also add a new intent to tell the handover
requested that a transfer has started, including the
count (if any).

Change-Id: Ib5e0e8dbc6c2e3259e0f732a507557c3688e168c