Fit/FitMap initial values

[keara-soloway]

CHAP.utils.fit.Fit[Map] have some issues with delivering the parameters' initial values:

FitMap --

• FitMap.init_parameters[param_name]['init_value'] does not contain the full map of initial values
• FitMap.best_values[param_i] does not contain correct values for parameters that are part of "expression" components (or maybe: any component that somehow gets excluded from the fit?)

Fit --

• Fit.best_parameters[param_name]['init_value'] does not contain the correct value for parameters with no explicit initial value set in the fit config.

@rolfverberg