mpegtsmux: add `stream-number` property on GstBaseTsMuxPad
This new property allows setting of PES stream number for AAC audio and AVC video streams.
The stream number is subject to the following constraints:
- it must be between 0 and 15 for video
- it must be between 0 and 31 for audio
Currently the PES stream number is hard-coded to zero for these stream types.
Edited by Aaron Boxer