Weather locations check in Region class

[SabineHaas]

In the new feedinlib it is planned to be able to use available weather data as well as your own data.
In the Region class it is looped over the weather locations. It would be nice to get a warning if the weather locations are very far away from the power plant's location (maybe a km range as parameter). This would prevent bugs by entering the "wrong" weather data or in case users enter power plant locations not covered by the available weather data.