[Actions] Move the remaining actions out of MediaWiki::performAction into single...

[Actions] Move the remaining actions out of MediaWiki::performAction into single action classes (finally).

- [Actions] -
* I am aware that eventually these classes should be more than just a few lines re-directing control to WikiPage, but I'm keeping these commits as uncontroversial as possible due to feature freeze. Refactor could be done later.
* Contributes to solution of bug 27930 - Ablity to get current action (The Right Way)
* Final goal: Get the current action without needing access to Wiki.php internals (i.e. with Action::factory in one hand and an instance of IContextSource in the other)
* Required for proper fix of r108342/108343 (currently marked FIXME)