(Re-)Add ability to work even if preference is hidden

We want to mark the preference as hidden as we then subsequently remove it.
However, if a preference is hidden and we don't set ignoreHidden=true, then
it will always fail to trigger VisualEditor, which is sad. Consequently, add
this awful hack until deployment of VisualEditor is true for all wikis.

(We may want to refactor this enablement code a bit - it's a tad ugly. I've
added some more spacing just so you can see what's what, but…)

Change-Id: Ia43c9241b53dddb3dcb8b3edfb3b5163e19e18b1