Fix for showing a creature as tapped while in a group

- Ported mangos code for Player::isTappedByMeOrMyGroup
- Ported mangos code for Object.cpp for setting the UNIT_DYNFLAG_TAPPED
  and UNIT_DYNFLAG_LOOTABLE flags
Fix for looting non-FFA quest items in group

- Added quest_item_added member to LootItem struct
- Use quest_item_added to track if the quest item has been added to the
  creature's loot rather than overloading is_blocked
- Using is_blocked was causing the loot to always be shown as being
  rolled for while in a group
- Added a check in Player::isAllowedToLoot to return false if the
  creature no longer has any loot