Compliance Monitor: improve architecture

[mbuechse]

Separate business logic from request parsing, authentication, database operations etc.

Part of #633.

[mbuechse]

I started working on this, but I will now suspend this line of work because I see a lot of uncertainty with #660. Put differently, I think the code is now rather malleable (just because there is so little of it, and it is rather simple), and it should stay that way until we know what we want regarding #660.