Add fix for Windows 7N/7KN/or media features not installed

Ref:
https://github.com/johndyer/mediaelement/issues/444
https://github.com/johndyer/mediaelement/issues/677
https://github.com/johndyer/mediaelement/pull/868
Build JS
Overflow hidden on the positioned poster element
Delete mediaelementplayer.min.css from /styles/