earthobservations/wetterdienst: Move functionality to core components, use timezones for dates

Move more functionality into core classes Add more attributes to the core e.g. source and timezone Make dates of internal data timezone aware, set start date and end date to UTC Add issue date to Mosmix class that actually refers to the Mosmix run instead of start date and end date Use Result object for every data related return In accordance with typical naming conventions, DWDObservationSites is renamed to DWDObservationStations, the same is applied to DWDMosmixSites The name ELEMENT is removed and replaced by parameter while the acutal parameter set e.g. CLIMATE_SUMMARY is now found under PARAMETER_SET Remove StorageAdapter and its dependencies Methods self.collect_data() and self.collect_safe() are replaced by self.query() and self.all() and will deprecate at some poin