Added support for grouped selects

Added support for grouped selects. Definition is like:

      type: 'Select',
      options: [
        {
          group: "Standart",
          items: ["A", "AAAA", "CNAME", "MX", "SPF", "TXT"]
        },
        {
          group: "Advanced",
          items:  ["NAPTR", "SRV", "PTR", "NS"]
        },
        {
          group: "Special",
          items: ["Redirect"]
        }
      ]