Add hook SpecialCheckUserGetLinksFromRow

Hook creates extension point to adjust or replace the per-revision
links generated within CheckUser.  This allows extensions to provide
the most specific links desirable for CheckUser data.

The default generated links are provided to the hook as an associative
array.  This was done to make adjusting, rather than replacing, less
than a total pain.

Bug: 60275
Change-Id: Ib7848a222b6421536653e9661e622785780ec8ef
Merge "Add hook SpecialCheckUserGetLinksFromRow"