Refactor FactorModel class

[timtreis]

TODO(@timtreis)

• set_data_options(scale_views = False, scale_groups = False, center_groups = True)
• set_model_options(likelihoods, factor_priors, weight_priors, groups)
• .fit(epochs, verbose=1) 0 = nothing
• rename _factormodels -> factormodels
• combine two utils files

Maybe future:

• custom callbacks
• pass known covariates (like age so that we can regress out to get age-free results)

[martinrohbeck]

I like the treatment of the config options 👍