(Bug 48840) Create "smw-admin" right + "smwadministrator" group

Instead of using "delete" as right to access Special:SMWAdmin
use a new right called "smw-admin" to avoid having those
users with delete rights automatically accessing Special:SMWAdmin.

https://www.semantic-mediawiki.org/wiki/Help:Permissions

Bug: 48840

Change-Id: I0ee12192a646b370ac7671204d91e149c27c42bf