Improve tapping system + some fixes
- now the mob correcty switch the grey for players who is not tapped for.
- added more comment for tapping system
- fixe forget to release if loot is deleted (for exemple a player is looting a mob that disapear while he have looting windows opened).
- now if a creature have no loot it can be directly skinnable. (well on old version of retail we could see some empty loot windows, so i wonder if i need to implement it that way...)