Amino acids ambiguties are not handled correctly

[yaccos]

When running the function get_protein_mass_mapping_with_sbml I got the following error: KeyError: 'G8ZSL3' at line 141 in get_protein_mass_mapping.py. The key error does not trigger on all queries, but it does on the query with UniProt ID G8ZSL3. After a manual query (https://www.uniprot.org/uniprot/?query=G8ZSL3&format=tab&columns=id,sequence,mass), we see that this accession ID is valid, but has two amino acids ambiguties. Hence ProteinAnalysis will yield a ValueError which is handled by progressing to the next iteration of the loop. However, the dictionary uniprot_id_protein_mass_mapping does not get updated with the key 'G8ZSL3', which triggers the error when trying to access the entry later. I suggest you instead implement the solution I suggested in #8 (comment), because even though two amino acids are ambigous, UniProt can still find a reasonable protein mass. Alternatively, you could replace the ambigous amino acids from the string before feeding it into ProteinAnalysis, which will still give a good esimate as ambigious amino acids consititue only small fractions of proteins.
https://github.com/ARB-Lab/autopacmen/blob/69a158003d5bab3f597ec5da727515d250f35a43/autopacmen/submodules/get_protein_mass_mapping.py#L133

[Paulocracy]

As described in my comment in #8, I just merged your proposed solution into the master branch, which should fix this issue.