Adds /v1/names/ response for pending names

[kantai]

Addresses #7 --- when a name is pending (a batch containing the name isn't issued yet) or the batch has been submitted, but not picked up by indexers yet, the registrar will respond to /v1/names/ lookups.

For pending names, the status will be "pending_subdomain" and last_txid will be an empty string. For submitted names, the status will be "submitted_subdomain" and last_txid will be the txid it was submitted in.

Examples:

$ curl -q localhost:3000/v1/names/potato.testing_test.id | jq .
{
  "blockchain": "bitcoin",
  "status": "pending_subdomain",
  "last_txid": "",
  "zonefile": "$ORIGIN potato.testing_test.id\n$TTL 3600\n_https._tcp URI 10 1 \"https://gaia.blockstack.org/hub/1PQs1WF5BPDM7bT85z2TBaLCofsnGBEatb/profile.json\"\n",
  "address": "1PQs1WF5BPDM7bT85z2TBaLCofsnGBEatb",
  "zonefile_hash": "81637262dfde7bbf774ccb60964c02a610acac18"
}

$ curl -q localhost:3000/v1/names/aaron.testing_test.id | jq .
{
  "address": "16LPutBwZQXy9BypANh1q2y5Z5fpwrmifp",
  "blockchain": "bitcoin",
  "last_txid": "ca18e86b06660db934a697ed417e650988ba4a9da4296d155d55909400dda3fb",
  "status": "submitted_subdomain",
  "zonefile": "$ORIGIN aaron.blockstack_berlin.id\n$TTL 3600\n_https._tcp URI 10 1 \"https://gaia.blockstack.org/hub/16LPutBwZQXy9BypANh1q2y5Z5fpwrmifp/profile.json\"\n",
  "zonefile_hash": "320d7c7cc5c0be10da74a9eb487e4c216982118a"
}