feat: add uploaded and created by to definitions and exercises

### Additions

* add field `uploadedBy` to `DefinitionType`
* add field `timestampCreated` to `DefinitionType`
* add field `maintainers` to `DefinitionType`, this field returns the same data as `userSet`
* add field `createdBy` to `ExerciseType`
* add field `timestampCreated` to `ExerciseType`
* add field `instructors` to `ExerciseType`, this field returns the same data as `userSet`
* add field `users` to `TeamType`, this field returns the same data as `userSet`
* add field `uploadedDefinitions` to `UserType`
* add field `createdExercises` to `UserType`

### Changes

* deprecate field `userSet` on `DefinitionType`
* deprecate field `userSet` on `ExerciseType`
* deprecate field `userSet` on `TeamType`

Closes #208