Features
- Make level moderation proactive
([1773](https://github.com/ocadotechnology/rapid-router/pull/1773),
[`42196e2`](https://github.com/ocadotechnology/rapid-router/commit/42196e287aef3b7e119c7ca62af12140c4bcfed7))
* feat: Make level moderation proactive
* Clean
* Migration
* Remove icon and fix redirect
* Fix tests
* Reuse variable
* Student can only access approved levels
* Approval needed by default, set exceptions and constraints
* Logic fixes
* Notify teacher on creation