Improve performance

[praseodym]

The avarage GET /api/v1/course/active takes 450ms (p90) and does 1046(!) SQL queries. This one comes up a lot:

select exam0_.id, exam0_.course, exam0_.date, exam0_.including_answers, exam0_.name from exam exam0_ left outer join course course1_ on exam0_.course = course1_.code where course1_.code = ?

I think simple some optimisations (eager fetching) should take care of this and improve performance.