add a check for the station id to Network.get_response()
refactoring obspy.station.inventory.Inventory.get_response()
basic tests for Inventory.get_response() and Network.get_response()
only call get_response() on Networks with matching id
Merge remote-tracking branch 'kaeufl/releases' into releases

Also some refactoring, flake8 etc.

Conflicts:
	obspy/station/inventory.py
Merge remote-tracking branch 'upstream/releases'