Add link generator function

[loraine-gueguen]

in lib/sequenceserver/links.rb, see https://sequenceserver.com/doc/#plugin

For sulfatlas :

SULFATLAS_ID_PATTERN = /([0-9A-Z]+)_S\d(_|-)\d+/
[...]
    def sulfatlas
      return nil unless id.match(SULFATLAS_ID_PATTERN) or title.match(SULFATLAS_ID_PATTERN)
      uniprot_id = Regexp.last_match[1]
      uniprot_id = encode uniprot_id
      url = "http://abims.sb-roscoff.fr/sulfatlas/result.html?term=#{uniprot_id}&field=shortUniprotId&type=exact"
      {
        order: 2,
        title: 'Sulfatlas',
        url:   url,
        icon:  'fa-external-link'
      }
    end