Add N-terminal methionine check to manufacturability

[julia326]

From manufacturer, for a particular variant:

"Peptide 2 and 3 ... were selected for production since peptide 1 contains an N-terminal methionine, which is prone to oxidation during synthesis, purification and storage."

[julia326]

Going to add to this issue as manufacturing concerns come up that we don't already address in our code.

We should avoid C-terminal glycines: "Peptide contains a C-terminal glycine which can be prone to side reactions during resin loading."