[Feature request] Toggle menu with keyboard shortcut

[UnoSD]

Hi again :),

can you please also consider making the keyboard shortcut toggle the menu? At the moment if I press SUPER I get the menu, if I press it again nothing happens and I have to use ESCAPE. The toggle behaviour is consistent across whisker menus (see mintmenu, Windows menu) and it's actually quite natural.

Thanks.

[ranjan-purbey]

Refer #70
The solution by vkareh works perfectly.