Make Special:Unblock link to contributions page for IP blockees

Currently, Special:Unblock links to the user page of anon editors,
which is inconsistent with other areas of the software,
and also less useful, as IP userpages are often redlinks.
This patch converts these links to Contributions links.

Originally reported on Wikia, with an (incomplete) patch here:
https://github.com/WikiaVolDev/app/compare/VOLDEV-31

Change-Id: I0fc73c7ee4fd7c81ed876717e8f60749c51685ae