Implement optimization problems

[meisterT]

• This is meant for problems where there is no "correct" answer.
• The grader spits out a (float) number that is representative how "good" the submission is.
• The maximum of all submissions for that problem is taken as points for this problem.

(There could be variant where you take the minimum instead, but I would argue that the problem/grader could be changed so that it's always the maximum.)

It's not really clear to me how the Kattis problem format handles these, e.g. what is the spec for how to output points. Example problems welcome!

[meisterT]

Possible future extensions:

• allow combining with partial scoring: Implement partial scoring #2518
• allow combining with interactive problems