Add SpliceAI Scores to Variant Annotations

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SpliceAI scores would give more surface area for our surfacing of genomic context for variants. We should:

• Add a method of calculating/fetching SpliceAI scores for mapped variants
• Add a SpliceAI namespace to CSV export, or decide on an appropriate existing namespace to export this field
• Display SpliceAI scores in appropriate variant visualizations and fact sheets