Introduce the concept of primary and secondary weathers:
* Primary weather keeps the same behavior as previously across all weather providers, so it's non-breaking. This location is not necessarily the current location, just the primary weather location set by the user.
* The GenericWeatherReceiver now has a new extra WeatherSecondaryJson, that receives a json list with secondary weather locations.
It's guaranteed that the primary weather always exists, so the list of WeatherSpecs provided to devices is never empty. Update all support classes accordingly.
