SDK / exoplayer

1. Fix seeking in test2.mkv by handling non-default timescale
   after duration.
2. Fix handling of missing cues in test6.mkv by allowing playback
   to continue (but all seeks will reset to t=0).

Issue #631

Issue: #595

GitHub issue: #589

Issue: #589

The ID_SEGMENT can only be read once, as seeing the element a second time is
assumed to indicate that the file contains multiple segment elements (which is
not supported).

This change allows the element to be read twice if it is at the same position,
so that retrying loading from the start can succeed.

This ensures FLAG_END_OF_STREAM doesn't get permanently stuck.

1. Workaround for decoders that fail to handle the END_OF_STREAM flag.
2. Revert processing of final output buffer if it's non-empty. This
   introduced another bug (#596)

Reverts: b88012f5
Issue: #417
Issue: #596

SubtitleLayout no longer trigger re-layouts of the view hierarchy.
Instead, the SubtitleLayout just invalidates itself. This is made
possible by making SubtitleLayout a regular View that draws each Cue
directly onto the canvas, rather than having SubtitleLayout be a
ViewGroup with a child View for each Cue.

The SubtitleLayout is now properly aligned with the surface.
This means the subtitles remain on top of the video in portrait
mode, rather than being huge and below it.

Handling of this constant is already in place everywhere, this
just documents that its use is allowed.

Avoid using the VP8 decoder on Samsung Galaxy S4 Mini.
Issue: #548

Avoid using the MP3 decoder on Sony Xperia Z/API level 16.
Issue: #377

Issue: #585