Provide different share and commenting options for users

**Problem:**
Sanjida (user who wrote in a support request) would like to have the ability to share her annotations, but control the ability for people she's shared her annotations with to comment, view, or do both, so that she can customize the sharing experience based on the annotations she's made/the material she's annotating.

Take a look at the image below for more info. Zendesk ticket info here, and Dan's follow up as well:

https://hypothesis.zendesk.com/agent/tickets/850