Entity constructor can take a bunch of components.
Also, components don't necessarily need an entity.
Part of #34: Basic town screen with map

- Basic town with map and stairs
- Refactored creation of entities to use non-parent constructor
Resolved #34: Town + Stairs

- Draw player on top of everything (including stairs)
- Stairs that travel up and down (town/arena)
- addEntity returns entity for easy one-shot creation