this also allows using negative scores

get_submission_info_for_participants is primarily used by externallib.php

This change modifies the grading table to pre-seed record ids where they
already exist.

Where they do not exist, they are still fetched.

Thanks to Andreas Grabs for proposing a fix.

The problem here was that user/index.php checks the system level
capability moodle/site:viewparticipants when the user is on the front
page, and the moodle/course:viewparticipants on non-front pages.

But the navigation displayed the link by mistake even in situations,
when the user has the capability moodle/course:viewparticipants on the
front page (typically when the default role for the front page is set to
student).

Added behat tests for reproducing the bug and also for checking the
basic functionality of the feature.

Remove the csslint config, remove an invalid property.

Kept csslint ignore lines becacase stylelint seems to respect them and
more work will be happening on css cleanup in MDL-55372.

Don't try and fix existing issues, just prevent new ones landing..