Create an ArbCom group on the Czech Wikipedia

Creating a new user group with the 'browsearchive',
'deletedhistory', 'deletedtext' and 'abusefilter-
log-detail' user rights per community request
expressed in the bug.

Bureaucrats will be able to add and remove users
from this group; see bug for URL with on-wiki
consensus.

Bug: 61418
Change-Id: If02243453b723fd2cbcb1f066df359281009457a