added tile map class + refactoring for require

Added a tilmap class that handled json files exported by "Tiled"
It is able to render layers parallax

Here is an example for an actor that makes use of the tilemap class

```coffeescript
class TileMapActor extends LDFW.Actor
  constructor:  (game, @tileMapName, @tileSetName) ->
    super

    image = new Image()
    image.onload = =>
      data = game.preloader.get @tileMapName
      image = game.preloader.get @tileSetName

      @tileMap = new LDFW.TileMap game, data, image
      @counter = 0
      @scrollX = 0
      @scrollY = 0

  update: (delta) ->
    @counter++
    if @counter > 2
      @counter = 0
      @scrollY++
      @scrollX++
      @tileMap?.setScrollX(0, @scrollX)
      @tileMap?.setScrollY(0, @scrollY)
      @tileMap?.setScrollX(1, @scrollX * 2)
      @tileMap?.setScrollY(1, @scrollY * 2)

  draw: (context) ->
    @tileMap?.draw context

module.exports = TileMapActor
```