TextBlock style update 

Hi all,

This one passes tests and I ran through a few samples and it seems to behave as expected!

I did make a bunch of changes that I'll comment on inline which should be reviewed. I'm pretty sure this can be improved in a couple of places but I'm not sure how.

@jasonrclark I'm not sure how this should mix with #832. Based on what I see I think they should play nicely.
The trick was to rename the dsl version of style to `dsl_style` and reserve the `style` keyword for swt calls. That seemed great except that somewhere (the rspec errors weren't very helpful for me) the dsl still wanted a style method. So pointing that back to `dsl_style` seems to have done the trick.

I briefly experimented with naming the `gui` one `gui_style` but at the end of the chain `Swt::TextStyle` doesn't have a `gui_style` method, only a `style` one.