Fixes for my pull request that added MediaMetadata.GENERIC

Some time ago I created a pull request for MediaMetadata.GENERIC handling. It turned out that the code was not complete (long story but I couldn't properly debug it).

I've debugged the my code with someone else and it should now work (see link below for our discussion)

I am missing the changes I made since that last pull request I did so I think you might need to revert the revert?
https://github.com/GetVideostream/cordova-chromecast/pull/25

Anyways, if you have questions or if I need to do something I'd be happy to hear about it :)