Geo regions add command

`denominator geo add` adds the territories specified, if they don't already exist, to the geo group of a record set.

  * If you specify the flag `--validate-regions`, the input json will not only be checked for well-formedness, but also that the regions are valid for the provider.  Note that this may imply more remote commands against the DNS provider.
  * If you specify the flag `--dry-run`, only read-only commands will be executed.

Ex.

```bash
$ denominator -q -n ultradns-test geo -z geo.denominator.io. add -n redirects-us.geo.denominator.io. -t CNAME -g US-WEST-2 -r '{"United States (US)": ["Maryland"]}' --validate-regions --dry-run
;; in zone geo.denominator.io. adding regions {"United States (US)": ["Maryland"]} to rrset redirects-us.geo.denominator.io. CNAME US-WEST-2
;; validated regions: {"United States (US)":["Maryland"]}
;; current rrset: {"name":"redirects-us.geo.denominator.io.","type":"CNAME","qualifier":"US-WEST-2","ttl":300,"records":[{"cname":"elb-1234.us-west-2.elb.amazonaws.com."}],"profiles":[{"type":"geo","regions":{"Antarctica":["Bouvet Island"],"Canada (CA)":["Alberta","British Columbia","Greenland","Manitoba","Northwest Territories","Nunavut","Saint Pierre and Miquelon","Saskatchewan","Undefined Canada","Yukon"],"Mexico":["Mexico"],"South America":["Brazil"],"United States (US)":["Alaska","Arizona","Arkansas","California","Colorado","Georgia","Hawaii","Idaho","Iowa","Kansas","Louisiana","Minnesota","Missouri","Montana","Nebraska","Nevada","New Mexico","North Dakota","Oklahoma","Oregon","South Dakota","Texas","Utah","Washington","Wyoming"]}}]}
;; revised rrset: {"name":"redirects-us.geo.denominator.io.","type":"CNAME","qualifier":"US-WEST-2","ttl":300,"records":[{"cname":"elb-1234.us-west-2.elb.amazonaws.com."}],"profiles":[{"type":"geo","regions":{"Antarctica":["Bouvet Island"],"Canada (CA)":["Alberta","British Columbia","Greenland","Manitoba","Northwest Territories","Nunavut","Saint Pierre and Miquelon","Saskatchewan","Undefined Canada","Yukon"],"Mexico":["Mexico"],"South America":["Brazil"],"United States (US)":["Alaska","Arizona","Arkansas","California","Colorado","Georgia","Hawaii","Idaho","Iowa","Kansas","Louisiana","Minnesota","Missouri","Montana","Nebraska","Nevada","New Mexico","North Dakota","Oklahoma","Oregon","South Dakota","Texas","Utah","Washington","Wyoming","Maryland"]}}]}
;; ok
```