Adds the following additions to the toggle state endpoint:
- course override data from CourseWaffleFlag.
- computed_status for waffle flags (accounting for
course overrides when applicable), and waffle switches.
Note: the waffle switch computed_status will make more
sense when we include WaffleSwitch instances that don't
have any data in the database.
ARCHBOM-1429
ARCHBOM-1366