Unify property names in paypal service DTs
Bugfix: Don't perform merchant actions twice.
Merge pull request #656 from sharetribe/paypal-unify-dts

Paypal unify DTs
separated function from paypal_webhook to different controllers
draft for paypal preauthorize process
quick fix: (marketplaceservice) transaction.preauthorization_expire_at doesn't work with paypal
create 'initiated' transition state but exclude it from conversation
Use transaction_id form DB
Remove transaction_id from return url
Fix payment tab
Shortened references for Services