fix tests
no implicite reset of the model parameters in the initial guesser

Instead, call model.clear() explicitely before solver.solve().
This is much more transparent.
clear output parameters if a serious problem has occured

A serious problem is a problem which leads to an invalid spectrum.  In
this case the output masses / mixing matrices should be set to zero to
avoid confusion on the user side.
Merge branch 'development' into higgs-study
scan over m0 and TanBeta by default
adding NMSSM scan program