reserved groups

it would be useful to be able to mark groups as reserved, similar to tags and profiles, with subsequent permissioning. groups such as case resources are potentially referenced in the system, and we would not want them deleted by lower access level users.

the following patches achieve this:
https://github.com/nysenate/Bluebird-CRM/commit/836b762bece62dd5f20ab826179584368a47ff40
https://github.com/nysenate/Bluebird-CRM/commit/030f56e20c0c33a3c4910a66b0057836a7ea652c

in addition, we need to add the is_reserved column to the group table:
ALTER TABLE civicrm_group ADD is_reserved TINYINT( 4 ) NULL DEFAULT '0'

this patch assumes a new permission of "administer reserved groups" which would need to be added to the permissions list.
but we may want to discuss the merits of combining reserved tags and reserved groups into a single permission as they are likely closely connected in terms of permissioning usage, and it would cut down on how many fine grained permissions we have.