Hygiene: Use RL generated CSS

Adjust Makefile to generate the css file separately via load.php
Kill wgMFMobileImageRootDir and make Juliusz happy
Add stable class to body to deal with current transitional state of
chrome header.

Change-Id: I4ed96bf49f4ae26c85b0d8a901446695a089a0db
Merge "Hygiene: Use RL generated CSS"