Allowing UserJS and UserCSS within the Minerva skin

This change allows the use of User:X/minerva.js and User:X/minerva.css
bringing the Minerva skin in line with other skins. It does not,
however, include User:X/common.js or User:X/common.css since these
are typically intended for non-mobile interfaces.

The new user module can't be named mobile.user since there is already
a module by that name in MobileFrontend. Instead it is named
mobile.usermodule.

Change-Id: Iaa7345e4060427f76e27cebd7c0993afdb499059
Merge "Allowing UserJS and UserCSS within the Minerva skin"