Repurpose "plans" hotkeys to just change current sub-priority

[Dyrewulfe]

The "plans" keyboard shortcuts are, in practice, a non-functionality. As far as I can tell, there is no means to select a building from the "plan" with the keyboard. So, moving the mouse into the general area of the plan buttons is still required. I believe re-purposing these keys as simple sub-priority shortcuts would be of great benefit to smoothing out the user interface experience. I often find myself executing 'p'->#->[tool hotkey], and at times the priority overlay itself causes me issues with being able to see what I'm working on.