Added the progress dialog as a relatively generic thing (it was
implemented as a pair of dialogs in the WinForms version, for no
very good reason). Generation and assembler execution works.
These just needed to have methods added to the command definitions.
Also, added a style to the toolbar buttons so they fade when not
enabled.
Also, fixed the DataFileLoadIssue dialog, which was seriously broken.
I was setting the window size and letting the contents fill to fit.
Now I'm setting the content size and letting the window size itself
to fit around it. The latter feels like it'll hold up better as
things change.
