Allow for global renaming of users

* Adds Special:GlobalRenameUser for trusted users to rename
  global accounts
* Assumes that the user performing the rename has the ability
  to move whatever pages are necessary on the local wikis,
  including suppressing redirects
* Uses a new database table to store status and hopefully
  avoid race conditions
* Added hooks to prevent users from logging in or creating
  a new account if a rename to or from that username is
  in progress
* If a user is currently being renamed and tries accessing the
  wiki, their session is cleared.
* Adds Special:GlobalRenameProgress for users to check on the
  status of a rename, and which wikis are still pending.

Bug: 14862
Change-Id: Id78577e95d73fbcdcb72e80ef25a34106ac91aa2