Bug 48490: Report correct mode and whether to disable images or not

Move definition of wgMFMode into application.js
Move wgImagesDisabled into makeGlobalVariablesScript so it gets
added to HTML rather than JS which doesn't vary

Change-Id: Ic5f45299e57fa55f1b95ca1753a488b9c4bf7b18
Merge "Bug 48490: Report correct mode and whether to disable images or not"