Fix acceptance

* Fix acceptance info API to return user_id
* Adjust the url sent in the role / license acceptance email
  ```
  Change the url to <webview.url>/contents/<id>@draft/role-acceptance

  MANUAL-UPGRADE: Add "webview.url" to the ini file (e.g. development.ini)
  ```
`/contents/<id>@draft/role-acceptance` should be handled by webview without going to authoring.

The acceptance API in authoring is `/contents/<id>@draft/acceptance`, that needs to be added to the nginx rules.