Includes a bit untangling of the setup. Concurrent tests should not
overwrite each others user settings so one of the tests gets it's
own user.
Bug: T337862
Change-Id: Iae245063932d4c5d9e6b61c1fe102505d70c1039
Basic tests to show that the highlighting classes have been attached
to the expected elements.
TODO in later patches:
* tests for the wikitext 2017 editor
Bug: T270240
Change-Id: I01ebd9881d38dd877f19ee3bb4fdcbb74d43afaf