Move QueryPage and abstract subclasses to specialpage folder

... now that f508561f7bde ("Moved $wgQueryPages stuff out of the global
scope and into a function") has been merged, which eliminated hardcoding
of the pathname except in the AutoLoader.

WantedQueryPage is moved to a separate file.

Bug: 60445
Change-Id: If2019492722083819b82afa6302670b94b181098
Merge "Move QueryPage and abstract subclasses to specialpage folder"