There is basic support for muxing chapter information into the
Apple Quicktime format already, but there are two errors which
prevent correct detection on the player side.

1) A special apple 'text' atom needs to be included inside the
gmhd atom.

2) The *different* 'text' atom inside the 'stsd' atom needs a
proper header.

With these changes, the chapters are now picked up by Apple
players and reported correctly by tools like mediainfo and mp4chaps.

v3 Update: The stub TextSampleEntry creation is moved to where the
chapter track is created so it's now specific to this track.
Signed-off-by: Philip Langdale <philipl@overt.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>