Issue #381 clickable autocomplete

Made autocomplete to work with mouse.
I know the issue was created just a few hours ago. And was not yet approved by p-e-w. But I decided to implement it anyway. 
> I can't find any reference to double click event in Clutter. Is there one?

That's a very good question. I spent quite a while looking, and indeed I found that the `Clutter.ButtonEvent` object that you receive in the signal has a `click_count` property that counts the number of clicks in that "click sequence", so checking whether this is >= 2 should do the trick.

However, the docs have something weird to say about this: *"The clicks do not have to occur on the same actor: providing they occur within the double click distance and time, they are counted as part of the same click sequence."*

Still, this is obviously intended to provide double-click support so we should probably just use it.