Ed. 6 SegmenTemplate.Pattern for audio

[tobbee]

Pattern makes it possible to compress SegmentTimeline with cyclic patterns like audio in testpic_2s.

Implementation sketch:

1. New URL segtimeline_pattern/ value, complementing the general segtimeline_1/ to turn on the pattern
2. Same for segtimelinenr_pattern/, but using SegmentTimeline with $Number$ instead
3. If audio is not aligned with video, and a cyclic pattern is detected, pattern will be applied
4. The patterns should stay the same, independent of the start duration, and only the patternEntry value pE should change