Adding statistics for mentors.

[mikeoleynik]

General

Mentor will look statistic:

1. by students
   • tasks performed;
   • tasks not performed;
   • ...
2. by one task -> student
   • take time;
   • date;
   • ...
3. by task
   • number of students who completed the task;
   • number of students who not completed the task;
   • ...

User Stories

• Mentor in profile can look at his students and tasks;
• Mentor on student page can look at statistics by students;
• Mentor in task page can look at statistics by task;
• Mentor in task page can look at statistics by one task -> student

Backend

model Statistic, field: :complete (boolean), :task_id, user_id (counter_cache: ?)
Join table statistics