Support initData in MPD for ClearKey and Widevine
Created by: greg80303
Added a standard way to support initData in the MPD for both Widevine and ClearKey. A Widevine representative has confirmed that this is the standard way to format their ContentProtection element. For ClearKey, I have chosen to use the same format, since it is very simply and works well.
Updated the sources.json to add new test content for common encryption with and without init data present in the MPD.
Removed PlayReady/ClearKey content from the sources.json. IE11 does not support PSSH version 1 (which ClearKey requires). Just the presence of the ClearKey PSSH in the file causes an error, so we won't be able to test this combination of DRMs until the next version of IE (Spartan) is released.