If the main window was maximized before, maximize it when we
restart.
Changed the preferences to record the width of the right panels,
rather than the splitter distance, which is actually the width of
the middle of the screen.
Seems to work correctly on my non-uniform multi-monitor setup. I
added a check to confirm that the middle of the title bar falls in
the working area of the screen that WinForms thinks we're in, so it
shouldn't be possible to "lose" a window off the edge by dragging
it or by changing screen resolutions.
