Add Steem.Ninja to paid signup model. #399
This PR should add Steem.Ninja (https://email@example.com/steem-ninja-account-sign-ups-with-credit-card-and-referral-reward-system) to the paid signup model.
Steem.Ninja is an app provided by Oracle-D to buy steem accounts with a credit card. A new account currently costs 2$ and comes along with a 15SP delegation for 90 days.