Relatively straightforward, thanks to the way WPF ComboBoxes work.
Spent some time fiddling with the column width text boxes, but
ended up with essentially the WinForms approach.
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.
The disassembled lines are now shown in the custom-styled list view.
The DisplayList isn't being kept up to date on edits, but since we
can't edit anything yet that's not too limiting.
Pulled more code over, including the mostly-GUI-agnostic bits of the
source generation and assembler execution code.
