Renaming files to standardise files that are part of special pages.

Old names such as "CloseWikis.page.php" is not very descriptive at
all, and this commit moves the files that generate the Special pages
to a better naming standard such as SpecialClosewiki.php. The main
extension file is updated to reflect this change.

Change-Id: I871b3e4a466f270c92c0c1607118cd8580a4a040