(BugId:100980) - Fix losing categories inside of templates on save.
BugId: 100980 - added ParserPool::preprocess()
BugId: 100980 - use ParserPool instead of  in CategorySelectController
(BugId:100980) - Don't need to pass in wgUser, it is used by default.
Merge pull request #784 from Wikia/bugid-100980

(BugId:100980) - Fix losing categories inside of templates on save.