Add simple class that serves localhost in a thread

Useful to show the qcodes monitor without having to either run a subprocess or from the command line.

Example:

import qcodes
from qutil.ui import ThreadedWebserver
 
monitor = qcodes.Monitor(*params)
server = ui.ThreadedWebserver(qcodes_monitor_mode=True)
server.show()

Nb: goes nicely together with Firefox Side View