btn_pot_reset always reset the simulated Pot to the ambient
temperature. Add doubleSpinBox_pot_temp next to it (shown/hidden
together, same as the button) so the user can dial in a different
starting temperature before committing it - it seeds from the same
remembered ambient value on startup but is otherwise independent and
not persisted.
tasks/pot.py's PotTask.recv() now resets the plant to whatever
temperature the 'Reset' message carries, falling back to ambient for
the bare True a caller might still send.
jens
f035e1decd