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.
Extract some XAML icons from the VS2017 Image Library. There's no
particular reason to prefer XAML over PNG, but somehow it feels
more forward-compatible. (OTOH, defining images as ControlTemplate
instances is just weird. Yay WPF.)
