Add Wayland window selection GUI (take 2)

[dshoreman]

Adds a new list dialog using Yad to fix #42.

todo

• [x] Create dialog populated with list of windows
• [x] Enable selection of window and return choice
• [x] Show dialog only when called from keybinding

Second attempt. When I forgot to push a single "new" commit on develop before this branch, Github messed up the commit list on #44 and no amount of close/reopen/delete/push/force would fix it. Note to self: make sure you pushed develop before you push a new branch that bases off an unpushed commit :man_facepalming: