Ensure listing author has paypal account
can_start_transaction spec
TransactionService.can_start_transaction implementation
Ensure admin account is also verified
Ensure presence of min price and com percentage
admin_account is unused
Merge pull request #750 from sharetribe/ensure-author-paypal

Ensure listing author has paypal account
WTI
Add spec data for payment voided
Fix ipn data types
Add ipn handler and events for voiding a payment
Add handling for voiding a payment and events in success and error
Specs for voiding a payment
Move reject to transactionservice/transaction
Remove no-op branch.
Check for novelty data in ipn message
Add correct transition mapping for preauthorized => voided
Make ipn to use dependency injector in controller
Generalize payment update event and update only on changed data
Check that pending reason is external on transition