Change pupil page to include predicted budget,

This predicted budget is always independent of the original budget. The first value is calculated by the original budget and the predicted amount of students, and is only saved once users click "Lagre" on the pupil change form.
Afterwards this predicted budgetline should be included in the "TotalOversikt" graph. \

• Make a backend model for predictionBudget
• Make the current budget independent of any changes on the pupil form, submitting the form should only change the predicted budget.