Gave labels unique ids so they can be tied to checkboxes.

Labels were tied to the first dialog that popped up, when they should be tied to their own form (or context).

Fixes CNVS-16217

test plan:
- Go to any group
- Edit group settings
- Try to check/uncheck any checkbox by clicking on label.
- Go to other group
- Repeat

Change-Id: I0a25c52773458aa2242af1f43ae908060bc76ed1
Reviewed-on: https://gerrit.instructure.com/44218
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Andrew Butterfield <abutterfield@instructure.com>
Reviewed-by: Brad Horrocks <bhorrocks@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Brayden Lopez <blopez@instructure.com>