New feature: Jiggle by key click

[MalEbenSo]

Please add a fourth kind of jiggle: A (customizable) key click.

Reason:
When working with remote machines the first two jiggles do not work reliably for me, e. g. the idle time is only reset on the local machine but not the remote machine.
The mouse click jiggle works. But of course it clicks "somewhere" and I always have to remember to position the pointer in a safe position. So Jiggler is not launch-and-forget.

Something like F2 should work. But maybe others have other ideas about effective and harmless key clicks.

[Ben Haller]

It's a good idea. Jiggler is not really under active development, but if I do another update someday, I'll consider adding this.