Create breakout groups for LMS courses

**Defining "breakout groups":**
When instructors talk about breakout groups, they are typically looking for some or all of the following:

- A way to transition from full group to individual groups or vice versa, or both.
- A way to easily hide individual annotations from the group or expose individual annotations from the group.
- TBD

**Why do this?**
We've heard from a few instructors that they want breakout groups, both in ZenDesk tickets and in various calls. Some of the requests in ZD are found under the tag `lms groups`, which isn't descriptive enough, and the requests in webinars, demos, etc. are not recorded. This Issue can serve as a place to surface not only these requests, but refine what it is LMS users want from the groups experience.