Generic grader should report meaningful grades

[niotie]

Currently the generic grader only assigns grade 0, regardless of actual test results. Meaningful grades should be implemented.

[qcoumes]

I can try to implements these.

I'm thinking about making weighted test groups (default 1), containing also weighted individual tests (also default to 1).

[qcoumes]

I implemented the changes.

We have to think about the best way for the grades to interract with --failfast since every tests must be done to have an accurate grade.