Split loading extension ResourceLoader modules into its own function

Change-Id: If5d0b90e4867d573ab0712f578a7924e5a7a4887
Add support for a MediaWiki:GlobalUserPage.css

Many templates require CSS styles to display as intended, however
those styles are usually in MediaWiki:Common.css, meaning that
remote wikis may not have them. So, we add MediaWiki:GlobalUserPage.css,
which can contain those styles. It is loaded on the central
wiki's user page, as well as when displaying the remote page.

Change-Id: Ib31523bd973277ff3f8a86dbe96108a88cdc9975
Merge changes Ib31523bd,If5d0b90e

* changes:
  Add support for a MediaWiki:GlobalUserPage.css
  Split loading extension ResourceLoader modules into its own function