Region init

Added the ability to preset what a region map (and other layers) looks like in the layer style object in an init.json file.  If you drag in the public/test/init_test.json file and select SEIFA you will get a green colormap instead of the default.  This will be persistent across links as well. 

UI for fiddling with this is still missing, but should be a straightforward edit of the style object in the layer.

Also did  some clean up and broke out VarType into it's own file.