Decide what to do about circRNA and sgRNA

[afg1]

These two types have come up in the latest release, in accessions from ENA, somethimes with cross-refs.

We didn't set out to get them, so we don't really have a policy on whether they should be included or not. For now, they are in the database, but not included in the export to ensembl.

We should decide if we want these RNAs, and if we do, go find some additional good reliable sources for them.