Use VariantEffect in TranscriptAnnotation

[ielis]

Currently we represent variant effects as a strs in the TranscriptAnnotation. However, it would simplify the things down the line if we used VariantEffect enum members instead.

We need to require VariantEffects in TranscriptAnnotation and we should update all genophenocorr.preprocessing.FunctionalAnnotator implementations accordingly.

Definition of done

• VariantEffect enum is moved to the genophenocorr.model package
• use VariantEffect in TranscriptAnnotation
• update the FunctionalAnnotator implementations