Wikia block media node styling

VisualEditor.php
Added a new CSS file to the wikiaCore package to ensure proper order. 

ve.ce.Node.css
This is a new file with 2 selectors. First, the video play button receives absolute positioning for proper layout. Secondly, the z-index adjustment to local overlay (previously in init) was moved here with additional notes and a higher z-index.

ve.init.mw.WikiaViewPageTarget.css
Because ve.ui.Surface.css (part of the ext.visualEditor.core package) loads after this file and sets z-index on the local overlay, our z-index adjustments have been moved to ve.ce.Node.css which loads after the core styles.