Improve performance of database queries

[jpwahle]

This ticket aims to improve database access times by orders of magnitude by using indexes and efficient query design.

The ticket has some sub-issues to make migration in production easier.

1. Extend database schemas #90
2. Add caching to preRead, preUpdate, preCreate middleware. #91
3. Merge controllers of frontend with existing CRUD endpoints. #73

[jpwahle]

The filters are now almost instantaneous and the tool now more responsive in general #75.
The /quartiles functions are much improved too #74.

Still when quering without filters, the "worst case" is only better for /quartiles yet.
Other routes need to be made more efficient.

[trannel]

Related to or duplicate of #25