bug: default data handler
The station data handler tries to get the variables parameter (list), but loads it only from kwargs. But without an explicit statement, that this parameter is required, MLAir doesn't know about this requirement. As consequence, the data handler takes the keys of the dictionary. This is not a problem as long as the variables list is equal to a list of all keys from the stat per var dictionary. But this dictionary includes always the target variables. If this variable should not be part if the input space, the data handler will use the dictionary keys and therefore include the variable in the input space.
- Re-implement the station data handler as inheritance of the abstract data handler (and not the abstract station data handler)
- don't query variables from kwargs, but use it as a real keyword argument.
- check other parameters are requested from kwargs (they cannot work like this anymore since the invention of the advanced data handler concept)