Added command to set pane to last selected pane without a menu

[slagtermaarten]

Thanks for developing this awesome and useful plugin! This is a key command I would to have, could you merge this or adapt/rename it to something you think is better suited but achieves the same goal? Ideally, there would be an option to automatically set the target pane of each new buffer to the last selected pane. I mucked around with autocommands but couldn't get it to work just yet.