add naive anova predictor

[PascalIversen]

adds NaiveANOVAPredictor, a new baseline model based on a simple two-way ANOVA e.g. linear reg based on identities. No features used. Basically a mix between NaiveDrugMean and NaiveCellLineMean

for LPO GDSC2:

PearsonRResult(statistic=0.8972672876888541, pvalue=0.0)
vs NaiveDrugMeanPredictor (PearsonRResult(statistic=0.8277340222232414, pvalue=0.0))

For LCO the model is equivalent to the NaiveDrugMeanPredictor.

I think it makes sense to report any performance improvement relative to this baseline.

[JudithBernett]

Approved! But pls add documentation for the readthedocs

[PascalIversen]

done