Add an override button for the window-size

[KevinMcGee]

Right now the window size must be set by the user in the gui. For the CLI we state that this option is not recommended, so we should abide by those same guidelines in the gui.

The way it should work: The window-size will be turned off by default. If the user does not click the window-size override button the default model window-size will be used. If the user clicks the override button, the gui will take whatever parameters are set in the window size widgets.