(SP: 1) Fix offer terms for the student

[abalanovsky]

The terms of the offer must be fixed for the student.

Tutor has the possibility to edit its offer after students have already been enrolled in it.

It is necessary to record the conditions on which the student and the tutor have agreed, at the moment offer changes can affect:

• title
• description
• subject
• levels

Reproduction steps:

1. Create an offer (as a tutor)
2. Enroll on the offer (as a student)
3. Change the offer (as a tutor)
4. Watch the changes (as a student)

[TSlashDreamy]

@abalanovsky I don't understand it. If a student is already enrolled in this offer, then the student and teacher form a cooperation. Both sides can't edit cooperation at all. However, the tutor can edit the offer as he or she likes.

Screenshots preview

Edited offer (tutor side):  Accepted cooperation (tutor side):  Offers (student side):  Accepted cooperation (student side):