Count of correct answers per user

[verutrix]

We now evaluate correct answers but we don't yet count number of correct answers per user. Let's go for it!

[ZelenyMartin]

Sorry for the mess with approving your PRs. I firstly approve them, then I dismissed the approval. I left the comments in the PRs.

Also please create a PR to the quiz-tests. The tests were actually broken even before. Sorry.

[ZelenyMartin]

Also please when working on an issue with multiple PRs, have the branch name the same everywhere. I suggest format:

<initials>-<issue num>-<description>, so in this case: vt-23-correct-answers-count.

The reason for this is a future automation of CI on specific branches across multiple repositories.