Allow the camerabin source selection to be overridden.

Prefer the default camera-source element if there is one or an element
identified by an environment variable to a static list of possible
elements which may not be appropriate for the target environment.

Change-Id: I53816c949307953780f9046eb11e09effe059be0
Reviewed-by: John Brooks <john.brooks@dereferenced.net>
Reviewed-by: Andy Nichols <andy.nichols@digia.com>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
Fix configuration of camera settings in camerabin backend.

Enable gstphotography interfaces if the compile check passes, and
implement missing pieces of whitebalance and focus configuration.

Change-Id: Icd24dfd148204f8d8218176593c3120427a13e1e
Reviewed-by: John Brooks <john.brooks@dereferenced.net>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
Fix recording settings being discarded by the Camera QML type.

Query existing settings from the recorder instead of locally cached
settings as some other agent may have applied some settings separately
and those would otherwise be discarded.

Change-Id: I0ebeaf06c6f7306c5987aa269032842b538a6a8b
Reviewed-by: John Brooks <john.brooks@dereferenced.net>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
Fix playback with exotic gstreamer pipelines.

Extend the list of raw video formats, and allow the playbin flags to
be overridden by an environment variable when the default isn't
suitable for whatever reason.

Change-Id: I4c7d821b0ce29f5ad2dc0341e378ffd17c489e98
Reviewed-by: John Brooks <john.brooks@dereferenced.net>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
Only acquire resources as required in gstreamer backend.

Make resources required for capture optional and disable just the
capture features if they are not available, so the camera viewfinder
can be displayed and images captured without blocking the music
playback and the other way around.

Change-Id: Ic9692195156d994ccd4a911ae41d2242a00d575b
Reviewed-by: John Brooks <john.brooks@dereferenced.net>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>