Transaction entity
Move "entity" to datatypes
Instructions to create premier or business account

Changed PayPal instruction copys to point out that either a premier
account (for individuals) or a business account (for companies) is
needed to accept payments.
Merge pull request #678 from sharetribe/transaction-entity

Transaction entity
Merge pull request #679 from sharetribe/paypal-account-type

Instructions to create premier or business account
Draft of api spec for paypal payments
get payment info by transaction id
Use external merchant id, use symbols
Draft of accounts api spec
response bodies for token validation
Draft of billing agreements API
Billing agreement charge + reformat all
format Money types
Payments api skeleton
Add request payment implementation
Helpers for account and success response handling
Payments service, create and cancel_request
Payments using payments api (without authorization)
Update spec to require community id everywhere
Use community_id as path parameter