Errors in network analysis don't propagate and get shown in the UI

[dcabo]

#363 was caused by an error in the input data to the network analysis process. In this particular case, incomplete relations made the input format unparseable. #364 fixed that particular one, but the more general issue is that neither the user nor us the developers can see these type of errors. And, actually, there's another particular error lurking there: "closeness" seems to be undefined for "disconnected graphs", which triggers an error. (Should be a separate issue I guess.)