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)
  ```
Perhaps we should put all roles in the list, even those accepted. I imagine that would be handy for display purposes.

So this would become something like:
```
...
u'roles': [{
    u'role': u'authors',
    u'assignmentDate': formatted_now,
    u'requester': u'user1',
    u'hasAccepted': true,
    },
    {
    u'role': u'editors',
    u'assignmentDate': formatted_now,
    u'requester': u'user1',
    u'hasAccepted': true,
    }],
...
```