Update Media Element to add missing TODO's

[ne0rrmatrix]

I am wondering how much intererst there is in finishing the TODO's in media element.

TODO: Add support for MediaElement in an ItemsView on a Page containing multiple ItemsViews 
TODO: Add support for MediaElement in an ItemsView in a multi-window application

It is possible to add support for multiple windows to Android, iOS, macOS, and Windows. I am unable to test Tizen or work on that.
I figured out how to do both of those and I have tested them. I have them both working for ios and macos. The only issue is adding support for mulitple ItemsViews might be a bad idea? Do we want to add support for this? Is it not a bad idea to have mulitple ItemViews on a single page? Other than that I have it ready to go. It requires adding some additional code to traverse all windows and ItemsView and grab the correct one.