Removes insecure contacts API.
Updates the create contact flow to no longer require first and last name params (allows for more generic, wider-use contact creation).
Adds customer contacts API.
Updates sellers API docblock.
Adds seller contacts API.
Fixes alignment in contact service docblock.
Updates the contact validator to allow a numeric contact value for payment methods.
Allows an existing contact ID to be provided when creating a new payment method.
Allows an existing contact ID to be provided when updating a payment method.
Updates payment method update flow to use the core contact service.
Merge pull request #23 from volcano/feature/contacts-apis

New Customer and Seller Contacts APIs.