Adding support for timelapse capture using still camera's takepicture.

Also moving entire implementation into a new class CameraSourceTimeLapse
which inherits from CameraSource.

For timelapse capture using still camera, we start a thread which runs a
loop in which it calls Camera::takePicture() and then sleeps until the next
frame should be captured.
The function dataCallback() handles the callback from the camera with the
raw image data. This function copies the data and creates an artificial
timestamp corresponding to one frame time ahead of the last encoded frame's
time stamp. It then calls dataCallbackTimestamp() of the base class which
will think that it recieved the frame from a video camera and proceed as usual.

For moving the implementation to the subclass CameraSourceTimeLapse, added a
few virtual functions to CameraSource, which do the current thing for the base
class, but specialized things for CameraSourceTimeLapse.
E.g. startCameraRecording() in the base class just calls mCamera->startRecording(),
while in CameraSourceTimeLapse it may start a thread for the still camera case.

Change-Id: Ib787f24bd2e1f41681513f0257e1c4ca10a2b4de