Fix issue with moving a group leader in a raid

Moving a group leader to the ungrouped section was not correctly
finding an appropriate new group leader.
Handle Leadership with leader change in RaidCommandDisband
ndle Leadership with leader change in RaidCommandMoveGroup
Added clarification to 'drop_bots.sql' notes for cases of failed script
Implement group mentor, leadership exp sharing (SoF+ only)

Currently only works in normal groups
Some decisions: the EXP will be rounded in the favor of the group leader
No idea how live actually handles it.
Enable gaining of group leadership while in raids

Note: raid leaders can only gain raid leadership, so they won't
ever gain group leadership while leading a raid, even if they don't
end up gaining group due to the restrictions.

From what I can tell, this should be in line with live
Merge git://github.com/EQEmu/Server into Custom
C! Stun Resilience updates