Fix MW skin hacks

* Ensure surface widget font size matches main surface,
  move vector-specific hack to vector css file and fix.
* Fix base font size in non-isolated monobook windows.
* Move monobook z-index hack to global overlay only.

Change-Id: I1607dc77f81ac9c522e09a3b502aeb38fee02178
Merge "Fix MW skin hacks"