SDK / exoplayer

This prevents memory leakage even in the case where the app
is still holding a reference (direct or indirect) to the
Allocator.

Issue: #275

Github issue: #375

This package will house all extractors, which will be unified
to implement a single Extractor interface.

The limit on the ts packet buffer can be reduced during processing
if it's discovered to have padding. Hence we need to reset it back
to the ts packet size before processing each packet.

- Atom related stuff in Mp4Util is moved to Atom.
- Remainder of Mp4Util is renamed to H264Util.

- Keys should not expire during normal playbacks of correctly configured content.
- Attempting to refresh on expiration causes a race condition, that may result
  in either failure or brief re-buffer, for the 30s license test video.
- This change provides deterministic behavior, which is to always fail.

Some servers, probably edge cache machines that exclusively serve
chunked media, don't support partial requests. Which is kind of
vaguely reasonable for that particular case. This change modifies
DefaultHttpDataSource to correctly handle this case, by manually
skipping data up to the requested position (and making sure not to
read more data than the requested length).

better handling of input format change for non-adaptive codecs

The regex included quotation marks like X="YES", but the manifests
don't actually contain them, for examples X=YES.