Add new mediawiki/skins repos:

* Mask
* Splash

Change-Id: If102926c9ce585eb7830a97eb7ecaa02b486319c
Add sync-with-gerrit.py script, taken from mediawiki/extensions

Bug: 61732
Change-Id: I9f589bb5cf018c4e1130a3edb8294fcb319fa5fa
Merge "Add sync-with-gerrit.py script, taken from mediawiki/extensions"