DASH: Support http-head:2014 UTCTiming scheme

### [REQUIRED] Searched documentation and issues
I have looked at the previously reported issues on ExoPlayer and on stackoverflow as well.

### [REQUIRED] Question
I am working with live streams from a streaming provider in DASH format. The manifest file includes UTCTiming schemeIdUri="urn:mpeg:dash:utc:http-head:2014".

### A full bug report captured from the device
```
E/DashMediaSource: Failed to resolve UtcTiming element.
java.io.IOException: Unsupported UTC timing scheme
at com.google.android.exoplayer2.source.dash.DashMediaSource.resolveUtcTimingElement(DashMediaSource.java:896)
at com.google.android.exoplayer2.source.dash.DashMediaSource.onManifestLoadCompleted(DashMediaSource.java:801)
at com.google.android.exoplayer2.source.dash.DashMediaSource$ManifestCallback.onLoadCompleted(DashMediaSource.java:1290)
at com.google.android.exoplayer2.source.dash.DashMediaSource$ManifestCallback.onLoadCompleted(DashMediaSource.java:1285)
at com.google.android.exoplayer2.upstream.Loader$LoadTask.handleMessage(Loader.java:450)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.os.HandlerThread.run(HandlerThread.java:65)
```
### Link to test content