Small update to the group/party system.

- Fixes raid assistant privileges, Fixes issue #248
- Proper designation for Main tank and Main assistant roles
- Remove 2 redundant columns in DB, namely groups.mainTank and groups.mainAssist. These are now defined by the value of group_member.memberFlags

--HG--
branch : trunk

sql/updates/7515_characters_groups.sql

@@ -0,0 +1,3 @@
+ALTER TABLE `groups`
+DROP COLUMN `mainTank`,
+DROP COLUMN `mainAssistant`;