Support degenerate codons in translate table

[reece]

biocommons/hgvs#595 identified that degenerate codons are not supported by the translate function.

For the hgvs, this is a regression relative to prior versions that used biopython.

While this is being fixed, consider moving the translation tables to _data (i.e., here) to be accessed the same way that assemblies and cytobands are.

[stale]

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