Option to insert sequences from structures as additional sequences aligned to their reference sequence in the alignment

Potentially useful feature when focusing on available structure data would be to add the structures discovered/associated with a sequence as additional sequences in the alignment.

Several issues arise from this - explicit visualisation of the sequence/structure mapping in the alignment suggests they could be edited (which is probably not desirable, but might be for some cases) - so at the very least the group alignment needs to be managed as a representative sequence. That means that some or all the issues in JAL-2140 need to be addressed.