[Placeholder] Django admin pages to view and correct learner competency statuses

[jesperhodge]

Unresolved Requirements

• Django admin pages are needed to view and correct a learner's competency status, meaning the mastery status recorded for a learner at the competency level, and at the criteria group and criterion levels once Mastery status lookup + learner progress models #642 adds those models.
• Django admin pages are needed to view and correct the mastery statuses themselves, meaning the lookup table of AttemptedNotDemonstrated, PartiallyAttempted and Demonstrated.

Open Questions

• How do we implement downward corrections? An automatic write may only raise a status, while a staff correction may lower one (ADR-0004 Decisions 4 and 6), and [BE] Roll up a learner's competency status from criterion to competency after a grade is recorded #643 states that no current work covers the staff correction path. Should a correction include the tree rollup, and can that rollup cause the loss of statuses on higher criteria groups or competencies, or the loss of a mastery status the learner had earned?
• If a mastery status is changed by hand, how do we handle the tree no longer being in sync? The statuses above and below the changed row were computed from grades and from the old value, so they can disagree with the corrected row until something recalculates them.