Extract append query param to URLUtils
Merge pull request #723 from sharetribe/url-utils-append

Extract append query param to URLUtils
Update payments api documentation
Fix typo
Handle 10486

- Save redirect url to token
- Delete token only after successful authorize
- Add accessors to Token that take transaction_id instead of token
Add comma
Use merchant gem from PayPal repo
Merge pull request #722 from sharetribe/handle-10486-error

Handle 10486
Outlines for tasks
Remove unused method
Create callback hook for authorized
Implement token retries
Add authorization