Drop models_class1_processing_variants: replace models_class1_processing with what was previously models_class1_processing_variants

1.6.1

If the presentation models are downloaded but not the affinity models, use the affinity predictor included with the presentation models. Also, bump version to 1.6.1.

Version 1.6.0

Giving up on doctest in travis due to the small non-determinsm of predictions (i.e. last few decimals are different)