Use wmctrl (if installed) to raise and focus window.

[cben]

The code already tells skype to 'FOCUS' but that doesn't work, at least for me.
(I'm on Fedora 23 with Cinnamon desktop.)
wmctrl works perfectly, so added code to run it and text to README to install it.

I also tried telling skype to close then restore the window — this did raise it, but kept it below the currently focused one. And it didn't seem to focus it all all.
Adding this as fallback when you don't have wmctrl installed.

[cben]

Correction: if window didn't exist, wmctrl doesn't raise. On second run it does.
Might be a race condition, let's see... Yep, running wmctrl -l there shows sometimes the window doesn't exist yet. Let me try adding some polling...