Special page to manage global rename requests

As a steward
I want to have an easy-to-use, scalable interface from which to handle
  the Global Rename queue
So I can efficiently respond to the increased request volume expected
  due to SUL finalization.

Provides a new Special:GlobalRenameQueue page that can be used by users
with the 'centralauth-rename' permission to view/approve/reject requests
for account renaming made via Special:GlobalRenameRequest.

The feature is guarded using the $wgCentralAuthEnableGlobalRenameRequest
global flag.

TODO:
* Get email body text from Product

Bug: 68924
Change-Id: Id1adb8fb9e143d90df3621e342ab9e9ab34e7c9c