This behavior and API was extremely counter-intuitive since our default
behavior was for applications to never exit after you close all of their
windows.
Now that we exit the event loop by default when the very last GWindow is
deleted, we don't have to worry about this.
Here goes the first attempt at using VisualBuilder to make an application.
There are many features missing that we are gonna have to implement,
noticeably custom widgets (for the glyph editor and glyph map widgets)
but this patch already moves most of the UI layout to a form file. :^)
This patch adds a simple GMessageBox that can run in a nested event loop.
Here's how you use it:
GMessageBox box("Message text here", "Message window title");
int result = box.exec();
The next step is to make the WindowServer respect the modality flag of
these windows and prevent interaction with other windows in the same
process until the modal window has been closed.
