Implement an interface and abstract class to hold the widely-reused get(Request|User...

Implement an interface and abstract class to hold the widely-reused get(Request|User|Title|Lang|Skin|Output) accessors for objects acting as a context source.  Article is rather messier because both getTitle() and getUser() are in use for other things, and Article::$mTitle is in extremely wide use both within Article.php and outside.