Add Widevine support using the current webkit API. Also add the ability to set LAUrl, as Widevine does not store this in the initData.
Big thanks to @Hyddan for review and input, and thanks to @KozhinM @kirkshoop @dsparacio
Add @Hyddan changes to allow for cdmData and LA URL overrides using ProtectionData
Merge pull request #290 from xstreamnet/development

Add support for Widevine.

These changes are a result of several discussions and submitted pull requests. In particular #263 and #303 were influential. Also, thanks to @dsparacio for running WebEx calls for these discussions and everyone who participated.
Unlisten to needKey signal on media source teardown