Fixing group loot issue + chest loot issues

- Single players in group looting object above the quality of the treshold must now be able to loot them.
- Chests will now be excluded from the roll system, but not from the master loot system.
- Chests will now appear as "open" when a player has open it. Client will now display an error message in such case.
- Two players won't be able to open a chest simultanesouly like it was the case.
- Players will now appear as "looting" to other players while looting a chest.
Merge pull request #249 from Warkdev/Rel20

[Core] Fixing group loot issue + chest loot issues