Get rid of "devbox" database and create a way to run the code without wiki specific settings

This pull request is required to create maintenance script that will import ``wikicities`` database on devboxes.

It consists of:

* use ``$wgDevboxDefaultWikiDomain`` when no domain is provided (devname.wikia-dev.com) - defaults to corporate wiki (www.wikia.com)
* add ``$wgDevboxSkipWikiFactoryVariables`` that will disable wiki-specific settings loaded via WikiFactory
* small cleanup of Special_DevBoxPanel and devbox LocalSettings

Pinging @psychonaut and @owend for review.