Update ctr_informative_testing.R

Aanpassingen in de plot.InformativeTesting()
Update plot.InformativeTesting.Rd
Merge branch 'patch-11' of https://github.com/LeonardV/lavaan
Merge branch 'patch-10' of https://github.com/LeonardV/lavaan
better handling of empty.idx if missing="ml" in lav_data.R and ctr_estfun.R