Corect the warning message for unusual base leaving group

[ljubica-milovic]

Change to the previous ticket.

• If the user is making an Base monomer in the monomer creation wizard, and that monomer has an R1 attachment point with a leaving group different form H
  after clicking on Submit in the monomer creation wizard, they should get a warning message in a modal window: "Base monomers typically have a hydroxyl as the leaving group for R1. Do you wish to proceed with the current attachment points?" with options "Cancel" (default) and "Yes" and a title "Non-typical attachment points".