Install the frame callbacks on init not on set up pipeline
Install the frame callbacks on init not on set up pipeline

Previously the frame callback on the framebuffer and the new frame
signal from the sink were set up when the pipeline is set up, but I
can't see any reason why they can't be set up on init instead. That
will avoid accidentally setting up multiple callbacks if the pipeline
is set up multiple times.

bpeel/sprite-player,bpeel/sprite-player,bpeel/sprite-player