Moved the mp4 trimming logic into IsoFileContainerBox.trim_to_time_range()

All the logic that was in the main test function is now in
 IsoFileContainerBox.trim_to_time_range().

Fixed up lots of logging/output.

Tested with various range values with B-AVC_MP4_MP_SD-03.MP4 and verified
content playback with vlc.