Created and implemented getChosenBudgetCategories method + Disabled/Removed buttons depending on which budget window is shown

Savings and SavingsGoal classes with tests, implemented into GeneralBudget

See merge request !40

GeneralBudget set BudgetPeriod to be days left of month, and made FileHandling methods static.

See merge request !39

Created and implemented addUnusedCategories when switching scenes from budget + catch blocks display alert box

mini progressbars

edit or delete income/expense

Merge branch 'frontend-testing' of gitlab.stud.idi.ntnu.no:andreksv/idatt-1002-2023-9 into frontend-testing

IOexceptions