CreateInputsmodel [Breaking change]: do not allow to use `Qobs` on nodes other than Direct Injection and Diversion

With the introduction of Diversion nodes (#95 (closed)) arises the need to clarify the use of the parameter Qobs in CreateInputsModel.

Qobs is only necessary on nodes of type "Direct Injection" and "Diversion" which use a flow time series provided by the user. Until now, if the matrix had flows for other type of nodes they were silently ignored.

I propose to raise an error in the case of using Qobs on node other type than the ones which really need it. A simple warning can eventually be ignored by the user and can lead to errors difficult to debug since this case can come from mismatch column names.