Make sure mobile VisualEditor is only loaded when appropriate

On wikis that are VE opt-in, show the wikitext editor by default.
On wikis that are VE opt-out, show the VisualEditor by default.

Make sure we are only showing for appropriate namespaces and
not for pages that are the output of the Page Translation feature.

Make sure the switcher bar displays above the VE toolbar
elements.

Update browser tests appropriately.

Bug: 64681
Change-Id: Id801ae13206e8d927d06997b146c201f869758f3
Merge "Make sure mobile VisualEditor is only loaded when appropriate"