Improve keyboard navigation

This is a series of patches that both fixes some existing keyboard shortcuts and adds some new ones. With it, I can now use keyboard navigation for all of the basic things that I've been using frequently so far, which makes the experience a lot nicer for me.

(I use this in combination with a local hack that unconditionally sorts the room list alphabetically to avoid rooms jumping around when you pass over them with the cursor. I plan to turn it into an option and then I hope it should be mergeable, too.)