QA: KeepGoing browser tests

Much needed - all our keep going code is very brittle
For this to run:
Catpcha needs to be disabled for users
e.g.
$wgGroupPermissions['user']['skipcaptcha'] = false;
$wgGroupPermissions['autoconfirmed']['skipcaptcha'] = false;
You may need to toggle permissions of your Selenium user using
Special:UserRights

Changes:
* Adds a LogoutPage
* Simulates registration of a brand new user

Change-Id: Id922b8670f686c7a52a55f976b59f6d896d03069