Send notification when status of enrolment changes
Closes #608 (closed)
Design:
Step 1: Otto approves student to participate in the project (with no motivation)
User receives notification:
Step 2: Otto returns status to pending with motivation:
User receives such notification: 
Step 3: Otto changes motivation but does not change status:
User receives notification:
In the panel:
Edited by Anna Kalandadze