Loosen the paper policy

## References
* https://www.pivotaltracker.com/story/show/82119774

## Notes
This issue was raised because when an admin added a non-admin as a task participant, it did not show up on the dashboard.  This was because the paper policy was presumably too restrictive and the non-admin did not pass the `show?` policy logic.

So, this pull request is being opened purposely without tests because:  we have no idea what the proper policies should be in this case.  The change we made correctly shows the paper on the non-admin dashboard, but they would get `403`'d when trying to update the paper, for instance.  However, they would be able to update the task that they are now a participant on.  Is it acceptable to not allow updates on the paper if they are a task participant?  What should the other policy enforcements look like in this situation?

--- AC + TS