IMS-VT: Low battery handling for calls that can change to VT

1. For outgoing upgrade requests, seek user confirmation and
   as per user input, place the outgoing upgrade request

2. For incoming upgrade requests, if user tries to accept as
   Video, seek user confirmation and accordingly handle the
   incoming upgrade request

Change-Id: I8ea12a81b70e8e08a113d3c27721b17da65f0926
CRs-Fixed: 1091387
4 files changed