Tiles of different sizes are positioned incorrectly

[Elleo]

Currently the TiledScene uses a tile's own dimensions to calculate its cell position, this should be done with the map's tile dimensions to correctly place tiles of different sizes.

[Elleo]

Here's a quick example app in which this can be seen:
tile-fix-example.tar.gz

The tree top and trunk tiles are both 96x96, whereas the map itself is 32x32. This renders correctly in the Tiled Editor, but incorrectly in Bacon2D.

This is what it looks like at the moment:

And what it looks like after the fix in pull request #138 is applied:

[adderly]

+1