Port gstreamer capture plugins, video renderer.

As a side effect of not porting the same code two or three times over
this moves a lot of duplicated and often out of sync code to QGstUtils.
It also adds a new renderer plugin interface as the buffer allocation apis
have changed and aren't compatible with QGstBufferPoolInterface.

Change-Id: I0a86a5449600df8574eff6f831ce1591d8dd29db
MER: Add packaging.
Allow gstreamer to supply the default volume and muting of a stream.

GStreamer's normal default volume is 1.0 and unmuted, so explicitly setting
these values in the normal case isn't necessary.  In some unusual cases
changing the volume properties may change the application or global volume
and in those circumastances it's better to not change the volume.

Change-Id: I66130421f6096e396b748fcc651af20dff197eda
MER: Add enablers for working with camera rotation in gstreamer.

Includes a prototype control for reporting the orientation of the camera
sensor, and propagation of rotation information to the muxer element.

Change-Id: I7542cc54a253031b0692780f368cf31c65182d96
Implement customFocusPoint in camerabin backend.

Send a regions-of-interest event containing a rectangle surrounding the
focus point to the camera source when the camera's focusPointMode
is QCameraFocus::CustomFocusPoint.  Reset the regions-of-interest if the
focusPointMode changes to any other value.

[ChangeLog][QtMultimedia][GStreamer] Implement customFocusPoint in camerabin backend.

Change-Id: If75405733b18d476dff5467abae3f08271caf06a
Add a control which allows overriding the gstreamer video sink.

This enables applications to selectively use platform specific or
unusual (video4linux perhaps) gstreamer sink elements to render video.

Change-Id: Ife2c2f9b2149d6b598c69a78f1e116ba05b46e10