SDK / exoplayer

1. Change package name (rm "datasource")
2. Require injection of OkHttpClient through all constructors, and
   remove allowCrossProtocolRedirect/connectTimeout/readTimeout
   constructor arguments. The client should be configured with these
   prior to injection.
3. Fix code style to be consistent with the project.
4. Simplify call to get contentLength. I'm pretty sure okhttp returns
   the correct value when gzip is enabled, so there's no need to check
   this in the data source.
5. Misc cleanups.

Add an extension that provide DataSource using OkHttp

This change keeps the proportion offset * 256 as a floating point value rather
than rounding it before linear interpolation, which will increase precision
slightly when seeking in streams with XING headers.

In practice, this won't make much of a difference because precise seeking in VBR
MP3s with XING headers seems not to be possible without reading the entire file,
due to the fact that the (uneven) distribution of bits is represented by a fixed
number of table of contents entries.

Issue: #825

- The old approach was technically incorrect, because the checks
were "capacity < sampleSize" and hence neglected the fact that
the buffer position may be greater than 0 (e.g. if the caller
wants to prefix the sample with some additional data).

- Also proactively throw an exception if the buffer is too small,
rather than wait for the failure when we actually do the write.

This works around an issue where some devices, such as the Acer Iconia,
don't allocate large enough input buffers for H264.

Issue: #616
Issue: #714

Issue: #770

0 will crash. 1 is pointless.

....Except BACK and MENU, which only make sense if the the controller
is visible.

Issue #812

manifest.

Add onDrmSessionReady callback

This adds a callback for when DRM keys have been loaded.

Issue #804

Also include more Sony Xperia Z devices in the MP3 workaround.

Issue: #788

- Respect any padding set on SubtitleLayout.
- Allow specification of absolute, fractional and fractional-ignoring-padding
  text sizes.

Parse audioChannels only when on mpeg-dash