CaptureMotion: replace origin_frame_ptr_ by capture_origin_ptr_.

SO far, CaptureMotion was storing a pointer to the Frame where its MotionBuffer started. This was the Frame previous to the frame of the capture. The API of CaptureMotion reflected this with

• a const FrameBasePtr & in the constructor
• getter and setter for the origin_frame_ptr_ member.

Very often, algorithms needed to access not the origin frame, but the origin capture associated with the same sensor. This required a call to getCaptureOf(SensorBasePtr).

I find it overall a little odd. Storing the Capture everything seems easier: the Capture is accessed directly, and the Frame is obtained from the capture->getFrame().

So this MR replaces the pointer to Frame to a pointer to CaptureBase.

@joanvallve possibly this interests you as you were having a question about this short ago.