DAR-733 | DAR-284 | Special:Css saving content + delete/undelete/history buttons

https://wikia-inc.atlassian.net/browse/DAR-733
https://wikia-inc.atlassian.net/browse/DAR-284

New functionalities for Special:CSS:
* saving
* show changes
* delete/undelete
* history

Please do not merge until it's QA's finish their tests.