Actionable items

Adding ability to trigger events when pressing keys within proximity of obstructions. Define a `keys` object within the `proximity` object of an obstruction.

```coffee
  id: "fridge"
  src: "images/fridge.png"
  x: 1125
  y: 50
  proximity:
    radius: 60
    keys:
      action: ->
        EventBroker.publishEvent 'reactor:act', 'team_photo'
```

For simplicity's sake, the keys are predefined. "action" is spacebar, and the callback is fired if the current player is within proximity of the item.

This also adds the `Reactor`, which is basically just an event handler class. Check the `lib/actions.coffee` file for a list of actions by ID.