Improve window size/position

[DonCanjas]

vs-preview always opens in the same position, which has to be moved, resized or open in fullscreen mode. This can lead to having part of the window hidden. Adding a option to launch in fullscreen window mode to settings would be nice.

The first example is default vspreview. On the second, I relaunched vspreview after toggling some of the extra options. The window is too tall for my display so I am forced to resize manually or switch to fullscreen.

[Setsugennoao]

Should be resolved after #5d04108, which was requested in #34. Can you confirm?

[Setsugennoao]

Windows issue.