background style - not ready to merge

Hi all,

This is my next installment of addressing #711.

This branch works as expected and is almost ready to go in . . . except for a broken spec. (Comments in-line) Has to do with resource disposal . . . perhaps @jasonrclark can help? :)
(Not sure why I can't comment on line 33 . . . weird github thing . . . anyways)

Here's the error the specs throw:
```
1) Shoes::Swt::Background#dispose lets subresources go
     Failure/Error: expect(fill_gui).to receive(:dispose)
       (Double "fill gui").dispose(any args)
           expected: 1 time with any arguments
           received: 0 times with any arguments
     # ./spec/swt_shoes/background_spec.rb:33:in `(root)'
```

I wasn't able to figure out where `fill_gui` is supposed to get called in `Background` so I decided to pass this on to you guys, since I'm guessing @jasonrclark wrote this one.