add external reference temperature

[DOliana]

problem
When the sun is shining, the measured temperature is too high.

Describe the solution you'd like
Add a reference temperature. Idea:

• weather forecast temp is periodically sent to device (maybe hourly)
• if difference to actual temperature (including correction) is > 1 add additional corrective value (sensor temp - reference temp)
• this corrective value should only be used for some time (if no new value is sent). Example: only use reference temperature if younger than 60 minutes)

Describe alternatives you've considered

• add protective cover to sensor (sensor is already shaded - I assume higher heat comes due to adjacent wall being heated by the sun)

Additional context
A (wrongly) high temperature leads to the outside dewpoint also being too high, thus not turning on the fan.