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. 
Rather than running `get_selected_command` and relying on the hovering to select the item before we can click on it, this should retrieve the command to run based on `index`.

Actually, I don't think we should have hover-highlighting at all (most autocompletion systems don't).