refactor __str__ for SeismicStation
__str__ for Site
correct list properties of SeismicStation
remove "networks" entry from Network.get_contents().. network can not
really be a content of itself.. ;) if the description is to be included
in this dictionary it should get a different key like "description" or
"name"
check that Network.stations can only be set with Station object
check types when setting Inventory.networks
some work on ResponseList stage
docstring