#63 version 2.x: Save Saldi (of FReq)

[Anonymous]

It is quite dangerous that if you change some detail in a past month, and forget to "save saldi", the previous saldo (and thus the newly calculated saldo) in the next months are WRONG.
- Fast patch: empty the previous saldi after the month of the correction.
- Better: recalculate through all coming months after a correction.