[Plugin idea] Tag out new print jobs via print-surface dirty flag

Whenever the nozzle temperature exceeds the ooze threshold, set a flag. Whenever a user-configurable pushbutton is actuated (GPIO, usb hid, etc.), clear the flag. Optionally, show the flag via a user-configurable led-like output. Whenever a new print job is started by the UI or the API whilst the flag is set, nix the print job and send back a nice-looking error message (but keep the file loaded).