Move MainWindow to the screen the cursor is on

[inhinias]

A small quality of life improvement, that moves the MainWindow, upon launch, to the screen the mouse cursor is on.
This is useful on multiple monitors, so the MainWindow doesn't appear on a "random" screen.

[coveralls]

Coverage increased (+0.02%) to 6.973% when pulling f99b045 on JFK422:master into cbce15c on IJHack:master.

[coveralls]

Coverage increased (+0.02%) to 6.973% when pulling f99b045 on JFK422:master into cbce15c on IJHack:master.

[annejan]

Thank you!