[Feature request] Close windows by middle click

[WilliamCappelletti]

Feature request

It would be great to be able to close windows by middle-clicking on stackline icons, in the same way as tabs are closed on Firefox.

I did not ckeck your code, but I think that an easy way to implement this could be to remember current window, focus the target one, send an interruption message (this I am not sure about), and focus back to starting window.

Thanks for the great work!