Implement group mentoring while in raids (SoF+ only)

Note: This does not allow the raid leader to share raid leader XP
and since the raid leader doesn't gain group leadership, they can't
share that either.

utils/sql/git/required/2014_10_19_raid_group_mentor.sql

@@ -0,0 +1,2 @@
+ALTER TABLE `raid_leaders` ADD `mentoree` VARCHAR(64) NOT NULL;
+ALTER TABLE `raid_leaders` ADD `mentor_percent` INT(4) DEFAULT 0 NOT NULL;