Allow dropping multiple items at once

Fixes #970

Since std::queue is now used in a good handful of files, I've added it
to CommonIncludes.h
Better handling of missing items

If the player loads a save that contains an undefined item id, we now
create a blank "Unknown Item" and add it to the items vector.

Notable changes:

* fillEquipmentSlots() has moved from MenuItemStorage to MenuInventory.
Item's that can't find a proper slot are moved to the player's normal
inventory.
* If there are no loot animations for an item, we no longer crash when
dropping the item on the ground.
Only change sound state if different from current state.
Merge pull request #971 from dorkster/items

Better handling of missing items