[added] Group members can now assist a quest owner with quests as long
as the quest owner is in range of the target
[fixed] Quest items can no longer be looted from corpses by anyone but
the quest owner
[fixed] Quest targets killed by anyone but the owner and nearby grouped
members will fail the owner's quest and direct them back to the quest
giver
[fixed] Quest givers will send the appropriate message if they are
unable to find a valid location for the quest target

Change-Id: I7ff5970850143b4ca019f0ec27f3e287fa92dcbf