For mpd codes, rename dash_packager to edash_packager; for media codes,
add namespace edash_packager.
Change-Id: I1120e6110c734cd02bdbe15f1cf7abddcdfdd7ea
Renamed EncryptionKeySource and WidevineEncryptionKeySource to KeySource and
WidevineKeySource respectively.
Replaced Initialize method with FetchKeys.
Added unit tests.
content_id parameter is now binary. Specified in command line with hex string.
Change-Id: I8010ca62d036cefb3a7c105e0eefee25bbf06d61