POI Mode: Add a "POI" input mode for the CameraStab channels and the objects to support them

Conflicts:
	flight/Modules/CameraStab/camerastab.c
	flight/targets/Revolution/UAVObjects.inc
	ground/openpilotgcs/src/plugins/uavobjects/uavobjects.pro
POI Mode: Add a stabilization mode "POI" which only safely applies to Yaw (needs sanity check added)
which takes the CameraDesired.Bearing and faces it.

Conflicts:
	flight/Modules/Stabilization/stabilization.c
	shared/uavobjectdefinition/manualcontrolsettings.xml
	shared/uavobjectdefinition/stabilizationdesired.xml
POI Mode: Only update the POI Location on change
POI Mode: Add to the sanity check conditions and add a flag to enable the POI tracking feature
Camera Stab: Tracking POI location to a tablet location

If a tablet is connected and pushing its location (TabletInfo) and the
mode is set to CameraPOI then the camera stab module will convert that
position into NED coordinates and set it in PoiLocation.
GCS Relay: Never allow forwarding messages from GCSTelemetryStats remotely

If this message can be forward it causes handshaking.  This triggers repeated
handshaking before the main and remote GCS.
VtolFollower: Add an option to select yaw behavior

Now during navigation (path planning or position hold) the
yaw can either be rate, axis lock, or follow the point of
interest.
Camera Tracking: Process tablet updates with rest of information

Only enable tablet callback when needed

Previously converting the tablet position into NED location was
run within a callback which isn't ideal, and also would run as
often as it updated - regardless of how frequently it was used.

Now it is within the camera thread (unfortunately still a callback)
but only when needed and at a limited frequency.
Camera Tracking: Remove a debugging offset
CameraStab: Only track objects more than 2 m away

Much closer can lead to invalid estimates of angles
Camera Tracking: Allow POI mode for yaw on higher end platforms

Previously the define was hardcoded into the module which meant the
sanity check didn't check properly and all airframes needed it.
Camera Tracking: Updates from review comments
Stabilization: Check that CameraDesired exists before using

When using POI mode it is possible that the CameraStab module is
not running so we need to check this handle to avoid a segfault.
Set an error in this case, but ideally this should be handled in
SanityCheck.  Currently it is for normal modes but not for
navigation.  However the later case is less critical since if you
can use this POI heading mode it is probably safe to leave alone.
Merge branch 'james_development' into camera_tracking

Conflicts:
	flight/Modules/Stabilization/stabilization.c
Camera Tracking: Update a RAD2DEG to use the constant
Merge pull request #408 from peabody124/camera_tracking

Camera tracking