ui improvements

* add png backgrounds to layers
* get rid of checkboxes and radio buttons -- use color to show toggled state
* add some styling to new UI -- change mouse cursors; some drop shadows; restyle buttons

I like the map layers styling with backgrounds; I'm not sure how I feel about the models submenu yet... 

I think the touch UI poses new design challenges and we'll have to evolve the older UI to be more touch friendly. Enlarge buttons, etc.