VariantTranscriptAnnotation - subtly show errors with overlapping transcripts

We show a list of transcripts to select from on the classification and variant page.

Some of these will fail as they are not valid c.HGVS coordinates (off transcript etc)

They may have worked in PyHGVS but now won't in Biocommons hgvs

We currently swallow any errors and display "?" but we should perhaps say why they can't do it (coords off etc)