Don't allow highlights in a restricted group that the user is not a member of

Closely related to #2338

Currently, in the following scenario:

* Current user is viewing content in a restricted group (i.e. has a restricted group "focused", or selected)
* The user is logged in but not a member of the restricted group
* The user highlights some text in the page and clicks "Highlight"

## Current Behavior

Creating the highlight "appears to work" and will show up in the sidebar under the current restricted group. However, upon reload the highlight disappears as the current user is not authorized to create annotations or highlights within the restricted group.

## Expected Behavior

TBD. This situation is nuanced: what _should_ happen?