Move budget file selections to wizard module
Clean up MainWindow
Rename BudgetFileWizard to BudgetSourceWizard
Add initial budget source classes
Use BudgetSource in UI
Add handling of unsaved changes
Add failure-to-open-budget error handling
Add initial integration of budget with UI
Add undo/redo functionality to MainWindow/Session
Add initial budgeting period classes.
Add unit tests for BudgetingPeriod
Integrated budgeting period with budget
Create initial edit-budget widget
Add initial balance field to budget details.

Also create initial draft of a money editor widget.
Add multiple currency support to MoneyEdit
Create custom LineEdit widget to remove undo/redo
Make name field a LineEdit instance to remove undo/redo
Remove undo/redo from line edit context menu
Fix behavior bug when typing into LineEdit
Add budgeting period form to budget details form