currently needs ~ -1 + c(factor) + factor or ~ -1 + c(1) + c(factor) + factor to do the sensible thing, should just need ~factor)
breaks down for more than 1 factor as no reference categories are defined and model becomes rank def., currently need to set up dummies manually and use those....
see dev-multiple_factors, check constraints used in FDboost...
~ -1 + c(factor) + factoror~ -1 + c(1) + c(factor) + factorto do the sensible thing, should just need~factor)