PDBe REST api now (v1.8) provides uniprot_canonical flag

> /mappings/all_isoforms/
>     + is_canonical field added (true if the UniProt sequence is the canonical
>     one, false otherwise).
>     + The call now accepts UniProt accessions as input, including isoforms
>     (e.g. P83949-5).

The latest version of the PDB REST API flags whether a UniProt isoform is canonical or not. This is relevant to ProteoFAV.