Poll a queued request

States are queued, live, or declined. Live means rows are ready; declined means stop polling. While queued, automatic_attempts_left: false (and poll_again_in_seconds: null) means the automatic runs are finished and further polling will not change the answer. When the request has a pot, the response adds bounty_id, pot_status, pot and subscribe_url, and pledge_url once the pot takes money. While pot_status is needs_fixtures it takes no money yet: pot_waiting says who adds the example answers and what happens next, pot_contract_url is there only when this caller can add them without paying (the key that created the request), and pot_open_url is there when anyone can open it: POST it with amount_usd and contract, and the pot opens with that contract when the payment goes through.