new naming for .nc files using keys of statistics per var, remove var_all_dict...

new naming for .nc files using keys of statistics per var, remove var_all_dict due to no usage inside program, check target var and remove unused keys from statistics per var

src/data_handling/data_preparation.py

@@ -138,10 +138,12 @@ class DataPrep(object):
         return xarr, meta
 
     def _set_file_name(self):
-        return os.path.join(self.path, f"{''.join(self.station)}_{'_'.join(sorted(self.variables))}.nc")
+        all_vars = sorted(self.statistics_per_var.keys())
+        return os.path.join(self.path, f"{''.join(self.station)}_{'_'.join(all_vars)}.nc")
 
     def _set_meta_file_name(self):
-        return os.path.join(self.path, f"{''.join(self.station)}_{'_'.join(sorted(self.variables))}_meta.csv")
+        all_vars = sorted(self.statistics_per_var.keys())
+        return os.path.join(self.path, f"{''.join(self.station)}_{'_'.join(all_vars)}_meta.csv")
 
     def __repr__(self):
         return f"Dataprep(path='{self.path}', network='{self.network}', station={self.station}, " \