Add UniProt accessions for all subunits after next IMP release

[benmwebb]

PMI since salilab/pmi@91646dd supports reading UniProt accessions from the FASTA file. These are then stored in the IMP Model and written out to the RMF file, and can be used by the IMP.mmcif module when converting RMF to mmCIF. Add accessions to the tutorial (after the new IMP release which contains this functionality) so that we can demonstrate simple mmCIF file generation for deposition. Requires #35 to first be addressed.