This is to make it so that blocking all other admins is not
a succesful attack plan, as the blocked admins can block the
blocker, and then it ends in a stalemate with everyone blocked.
This also allows users with unblock-self right to adjust their
own blocks. The code already existed for this but was broken.
Credit for this idea goes to Tgr.
Bug: T150826
Change-Id: I0418279fdb2a59f8f1d7eeb8931d874123d03e4f
Make the necessary UI changes to Special:Block in order to set/update
partial blocks.
Bug: T197109
Change-Id: Ib3067824b5dcbdd893ab1f165d169a35d0716cb2
