Changed default gui app size to fit the layout

I'm really just putting this up for advice at this point. The window flashes when you startup or open a new file, which I presume is the initial window being set visible when the script gets added to `self.root()["scripts"]`, prior to my resizing.

Also, I wasn't sure how happy you'd be about me setting the size on File->Open. I think it's necessary though, otherwise we get that smaller size for anything but the initial app startup.