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.
So I think `gui_style` and `dsl_style` make sense to me here. The `:font_detail` part of it is what the SWT `TextLayout` class expects, and the `:font` is our incoming styles from the DSL.