WIP  REF: anova_lm

see #2123 and #1773 

This is not yet intended as "serious" PR

I had made some changes to anova_lm to extend anova_lm to GLM, but then decided to take a different route. There will be separate PR with `wald_test_terms` or `wald_anova` as generic method for ANOVA type 3 kind of analysis.