station: work on reading/writing stationxml
station: fix reading/writing of lists of float derived types, add option
to map additional attributes
station: safer output of pure float items (make sure output has full
accuracy)
station: fix handling of optional attributes name/resourceId, add
resourceId of stages subelement, rename stage_gain_value to stage_gain
station: work on writing response, refactoring and some fixing of
reading response