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? :)
SWT should just use dsl.curve, no need to create a new instance variable imo. The general idea is that the SWT backend just represents the DSL frontend and therefore takes all the front end data. The only data that it should keep itself is additional stuff it needs like actual created colors or whatever :)