TODO-370: faster opening from cold
TODO-370: faster opening from cold

Allows for valves that don't open until even 50%,
so that we get heat to the rads quickly when the room
is well below target.
opentrv/OpenTRV-Arduino-V0p2,opentrv/OpenTRV-Arduino-V0p2,opentrv/OpenTRV-Arduino-V0p2