CV4W GUI Dialogs not showing

[kfreezen]

This is related to #182, however there's a different root cause.

It appears that on some machines, the GUI is failing to open modal boxes completely.

A few ideas:

1. mainWindow handle is null -- this is debunked because BringAppToFocus() works fine.
2. BaseWindow.m_modalLock is locked, preventing any dialogs from being shown. I don't know how to debunk this one.
3. MahApps.Metro DialogManager has a bug and is not displaying dialogs in some cases.

[kfreezen]

The problem here is a combination of ideas 2 and 3. A bug in DialogManager occasionally prevents a dialog from displaying, which combined with the modal lock system, prevents any future modals from showing until a CV4W GUI restart.