applemedia: add support for MPEG-1 too
applemedia: improve usage of the VT API

Add timing information to CV samples and pass the GstBuffer
as extra data in the decode function
applemedia: fix segfault with dropped frames
applemedia: fix H264 streams with b-frames

The decoder output frames in DTS order, even with the flag
kVTDecodeFrame_EnableTemporalProcessing. We store a internal
queue of the decoded frames and push them PTS order.