movenc: Fix muxing of Apple Quicktime chapters. v3

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>
