Support for activity galleries

[brollb]

Corey Brady pioneered the use of NetsBlox activity galleries (as described here). It would be great to have tighter integration of them in the NetsBlox server so they can be managed by an owner have other configuration options. Here are some rough thoughts:

• Galleries should support comments and discussion around submissions. (Reactions?)
• Access to galleries may need to be restricted to only group members
• Submissions/comments may need to be able to be deleted (eg, for content moderation)
• Submissions should be able to be restricted. For example, submissions may only be allowed for a given window of time.
• Students may be required to submit before allowed to view their classmates' solutions.
• Submissions should be a snapshot of the projects (not a reference to a student-owned project).
• Users should be able to perform standard CRUD operations on their galleries.

[brollb]

• Expiration date for galleries