SDK / exoplayer

Issue: #400

1. prepare() needs to load a TsChunk to actually prepare the source.
2. Source is prepared, but no tracks are enabled (this is why it's
   an edge case - no-one is likely to be doing this!).
3. The TsChunk load completes.

We should not load additional chunks in this case.

Simple gradle updates

Partly fixes #434 as the AC-3 stream will now be ignored if the
audio capabilities don't allow it to be played back.

Issue #434

Issue: #423

Issue: #407

This allows loading a manifest from a file:// URI.

For Live SmoothStreaming, referential equality checking
isn't enough (it breaks once the manifest is updated).
Updated other instances too just for consistency.

Fix DataSourceInputStream.read() for EOF cases

Issue: #72
Issue: #292
Issue: #302
Issue: #425
Issue: #424

The spurious transitions were caused by calling pushTrackSelection
in onRenderers after changing the renderer building state to BUILT
and before calling player.prepare. pushTrackSelection can cause the
ExoPlayer to generate state changes, since it can call setPlayWhenReady.
This change transitions the renderer building state later, so that
when this happens getPlaybackState correctly masks the state and
returns STATE_PREPARING.

And delete things that we're parsing but don't use from TrackElement.

- This makes HLS consistent with Chunk/ExtractorSampleSource.
- It needs to be consistent for WebVTT in HLS.
- Also trim the allocator when done.

- Have TsExtractor report a SeekMap to the output.
- Implement TsExtractor.reset to reset extractor state.
- Add 1x sample.

Play movies has an Allocator that attempts to allocate a single
huge byte[] up front to minimize the risk of GC pauses. This abstraction
will be required to keep that when updating them to the new Exo.

Making Representation and TrackElement extend Format will simplify
this further (TBC whether this is a good idea!).

Issue: #393