moved Player and Maps storage into Dungeon class

- Dungeon is a global repository for storing the state of the dungeon as it is
  generated
- its also used to make the player a global reference
- stores a reference to the current map, as well as every generated map thus far
added inventory mixin for Player entity

- this should probably be refactored later on
  * Items share too many aspects in common with Entities for them not to be
    related somehow
  * The use() aspect of an item can be converted into a mixin of some sort
  * Though it seems unintutive, the Game.Mixins.Item could be abstracted into
    the class through isItem() and use() methods
refactored an Actor class

- Actor is made out of the differences between Entity and Item

		Glyph
		  |
		Entity
		/   \
 	     Item   Actor

- Actor contains the mixin system, as well as combat stats
created a messaging queue
created getItemsAt() to get multiple items
added pickUp to PlayerInventory mixin