APPWTV-25 and 14 Solved several issues with Playlists

Solved several issues with playlists, both on JS and CSS sides  
Now it is possible to navigate and select or deselect items in a playlist. This implied huge changes in SASS/CSS, AudioListItem.js, MediaSelectionColumn.js and MediaPlaylist.js. too  

Added remote webinosUi.app.deselectAt() as dual of selectAt()