Allow students to take debt on class creation/update, quantify it and report it.
Allow to register payments to cancel student debt.
As a starting point for this debt feature we will only allow to pay the entire debt. But the idea for next iteration is to allow partial payments (which is more realistic or it is a situation that could arise when operating with students). Reference to #12
Closes #8 Some changes reference #11
Summary
As a starting point for this debt feature we will only allow to pay the entire debt. But the idea for next iteration is to allow partial payments (which is more realistic or it is a situation that could arise when operating with students). Reference to #12