Correctly handle audio-only SmoothStreaming streams.
Correctly handle audio and video only DASH streams.
Don't require samples to specify whether they're encrypted.

This wasn't actually used for anything other than showing a
toast, which is now generated based on the manifest instead.
Partial support for DASH DVB Live streams.

- Adds support for dash manifests that define SegmentTemplate
  but no SegmentTimeline.
- Assumes that the device clock is correct when calculating which
  segments to load. The final step here is to use the Utc timing
  element in the DASH manifest to obtain an accurate client clock.
- Doesn't yet enforce that the client shouldn't load segments that
  are in the future or behind the live window.
Support DASH Live TTML subtitles.

Also add missing file.
Minor doc fixes.
Add initial AC3 passthrough support.