Support 7.1 EAC3 in MP4, DASH and HLS formats

[ybai001]

This update will provide below supports to ExoPlayer

• MPEG-4 with 7.1-channel EAC3 playback
• ID3v2 with 7.1-channel EAC3 playback, which used for HLS late binding
• Parsing DASH manifest with Dolby specific element

[ybai001]

This new pull request is based on the discussion in pull request 3085. I removed the 7.1 EAC3 TS handling part.
And update code based on two ojw28's comments.

1. file DashManifestParser.java: nit - Move this line(L909) to just above the switch statement (~L913)
2. file DashManifestParser.java: line 908, using Util.toLowerInvariant instead

[ojw28]

Now you're using toLowerInvariant on L908, these case constants also need to be lowercase :)

[ybai001]

Thanks. I'm stupid. :)
Case constants are lowercase now.