Move mediaplayer scripts into vendor folder

Includes moving app/assets/javascripts/mediaplayer/jquery.loader.js into
app/assets/javascripts/media-player-loader.js

New file has nomensa header deleted (duplicate of that in compressed
script) & all code removed that supports unused players.
Set player height to match existing
Merge pull request #205 from alphagov/mediaplayer-corrections

Move mediaplayer scripts into vendor folder