Implement additional fit measures

[jhorzek]

• rmsea
• likelihood ratio
• nfi
• nnfi
• aic alternatives

Especially for wls, we will have to implement additional fit measures.

[jhorzek]

Check https://www.researchgate.net/profile/Karin-Schermelleh-Engel/publication/251060246_Evaluating_the_Fit_of_Structural_Equation_Models_Tests_of_Significance_and_Descriptive_Goodness-of-Fit_Measures/links/0c96051ee93e8c1279000000/Evaluating-the-Fit-of-Structural-Equation-Models-Tests-of-Significance-and-Descriptive-Goodness-of-Fit-Measures.pdf?origin=publication_detail