Glide through menus with touch

[1j01]

On desktop (with mouse), I can switch to different menus by mousing over them during and after clicking to open a top level menu on a menu bar, just as in Windows. However, this doesn't work with touch. (I believe it worked in the past, although perhaps before os-gui was extracted from jspaint.)

Regarding: https://github.com/1j01/jspaint/issues/17