Submission/acolwell/media source

Update the contents of mp4/ to adhere to the ISO BMFF bytestream requirements:
- All 'traf' boxes have had their 'default_base_is_moof' flags set.
- Each video track has had an 'edts' box added to shift its samples' PTS back to zero.
- Buffered tests which push just the 'moov' box have had their size constants updated.
- Updated expected duration, location of initialization segments, and location of media segments of test.mp4.