Public description for private project

[saracarl]

This feature would be the ability to mark the description field of a collection as public, even though the project is private. The description could include instructions for joining the project.

We could even include a "request to join" button that would let logged in folks request to join the project (with an owner UI for approving). This would be useful for projects like ADAH's, zebrapedia, and classroom projects.

[benwbrum]

See #2402 and #2147 (possible duplicate)