Allow to resync balance (manually or automatic)

Created by: ZeHiro

I plan to import old bank operations in kresus (before the creation of the account), but this is currently not possible :

• The initial amount value is not dated (but could easily be by using the date of the youger operation, but what if an new imported operation as the same date as the current initial import date?

The origine of this problem is due to the fact that my bank only provides operations for the last 45days... (but I have the operations