Count of Graded/absent/total students and total lesson average mark in lesson view

[tomca32]

Above the students table in the single lesson view we should put one more card that would display aggregated information for total students that should have been in the lesson, number of graded(present) students and number of absent students. We should also include average mark for the all of those present. So basically add the all of the average marks of present students and divide it by the number of present students.

Student is considered present if they have at least one grade in any skill.

The order should be:
Total students, Graded students, Absent students, Average mark for lesson