Implement exposure and whitebalance lock for gstreamer camera.

Change-Id: I58277d69c18ad2e31cad719a2dd6361c0c2d7e98
Add additional exposure modes to QCameraExposure.

[ChangeLog][GStreamer][Android] Camera exposure mode extended to support
Action, Landscape, NightPortrait, Theatre, Sunset, SteadyPhoto,
Fireworks, Party, Candlelight, and Barcode modes.

Change-Id: I13d4bb042d27c0bd2ffcd369882b56bbabc84335