Allow redistribution and flexible adjustment of budgets

Currently, budgets are kept fairly static (i.e. they are created once with a fixed amount and then adjusted accordingly for the displayed period).

However, since e.g. income can change in a certain month, it makes sense to adjust the budget flexibly. It should also be possible to redistribute budgets, e.g. for a specific month, if you want to distribute all your income to the budgets.

In the future, when you edit a budget (e.g. the amount), you should be asked if you want to adjust all budgets or just the current and all future budgets. This would be similar to the behavior when you are currently editing a recurring transaction and the app asks if you want to adjust only the selected transaction or all future transactions. If you then adjust only the current and all future budgets (e.g. increase the purchase budget from $100 to $200 starting in July), you will still see the $100 budget as soon as you set the displayed period to June.

In addition, it would be useful to display the unplanned budget (income - planned budget [of the respective period]) instead of the "Available" area of the budget list, so that you can plan every euro. It would also be nice to be able to automatically distribute the unplanned budget to the individual budgets (e.g. as a percentage depending on the size of the budget).

Furthermore, it should be possible to define a starting amount for budgets and to automatically carry over unused budget amounts to the next period.