WIP restored non-fragmented trimming. Ready for MovieBox/fragment combo trimming

IsoFileContainerBox.trim_to_time_range() is now wired into the start/end-
 independent logic.

All IsoFileContainerBox/IsoMovieBox.*range() functions are deleted.

IsoFileContainerBox.get_random_access_point_for_time(),
 get_access_point_for_time(), and all delegated functions now take a
 sample_after_time param to return the sample after the passed time.
 Currently this is used for the IsoFileContainerBox.trim_to_time_range()
 end time calculation.

Added a IsoFileContainerBox.FileEndAccessPoint to designate when the range
 end hits the end of the file. This simplifies a lot of end-case logic.

Improved some of the SampleTableBox.AccessPoint is_at_start/end setting
 and logic.

Tested with boundary conditions on non-fragmented content files.