Updated mediawiki/extensions
Project: mediawiki/extensions/MobileFrontend  63245facc48a57593d172dfc3408ba295c260cd6

Don't nest .overlay-header and .overlay-head-container

Their names are unique enough and this will simplify styling of
position: fixed elements in VE.

Also consolidate 2 .overlay-header sections

Change-Id: I6faf60aed99ff6ad1d90603bbd12e19bda3ddf29