Pass $key into CommentStore methods and use MediawikiServices

Pass $key into CommentStore methods and use MediawikiServices

This allows CommentStore to be added to MediaWikiServices
without the need of an aditional Factory.

This change includes a compatability layer to allow the behaviour
from 1.30 to continue to be used while deprecated.

CommentStore::newKey has been deprecated.
Keys are now passed into the public methods of CommentStore
where needed.
The following CommentStore methods have had their signatures changed
to introduced a $key parameter, but when used in conjunction with
CommentStore::newKey behaviour will remain unchanged:
  * CommentStore::getFields
  * CommentStore::getJoin
  * CommentStore::getComment
  * CommentStore::getCommentLegacy
  * CommentStore::insert
  * CommentStore::insertWithTemplate

Change-Id: I3abb62a5cfb0dcd456da9f4eb35583476ae41cfb