Add allocation setting shortcuts

[morremeyer]

Is your feature request related to a problem? Please describe.

I want to set my budgeted amounts to:

• the average of my spend in the last year
• 0

Describe the solution you'd like

To make this easier, there should be an option to set all allocations for a month to average spend of the year before and one to set them to 0.

Describe alternatives you've considered

None so far

Additional context

This has been taken from #44 to this issue to reduce the scope.