Adapted the New Map dialog for Kodable maps

* Provide a choice between creating a 'Big' or 'Small' map
* Map is always orthogonal, using zlib layer data compression and
  its size and tile size can't be customized manually
* Automatically add 4 tile layers
Removed actions that modify the layer stack

Kodable has a fixed number of layers with specific names that should
always be there. No layers are allowed to be added or removed. I've also
assumed reordering and renaming is not allowed.