Define sequence mappings and propagate references using pairwise alignment

The 'Fetch DBRefs' mechanism often fails when a source of an alignment uses a sequence that is different to the one reported by the sequence databases. When one simply wants to view information mapped onto that sequence, it would be nice to retrieve the correct reference sequence and generate a map from the reference sequence to the one in the alignment using the 'paiwise alignment' dialog.

GUI Modification: add a 'transfer reference annotation' or 'create reference mapping' function to the 'Pairwise Alignment viewer' dialog that adds a mapping from the reference sequence to the aligned sequence.