mjpeg: Split off bits shared by MJPEG and LJPEG encoders

This obviates a dependency of the LJPEG encoder on mpegvideo.
dsputil: Split off IDCT bits into their own context
Update Fiona's name in copyright statements.
mov: Support default-base-is-moof.

default-base-is-moof shall be set to track fragments compatible with DASH
Media Segments. So, this is a fundamental support for ISOBMFF ver. DASH.
This is meaningful only when base-data-offset-present is absent and two or
more track fragments are present in a movie fragment.

Signed-off-by: Martin Storsjö <martin@martin.st>
vaapi: Update idct_permutation location after dsputil/idctdsp split
matroska: K&R formatting cosmetics
matroska: Factor out write_track from mkv_write_tracks
matroska: Factor out mkv_write_stereo_mode