* Entities
** payment schedule (name occurence amount)
** payment (payment-schedule date )
** transaction (amount date)

* Use cases
** Set income dates
Store dates for periods calculations

** Add payment
Set name, schedule (due date), amount. System calculates required per-period payments to get the
 amount till due date.

** Transfer money to
Update balance, top up all pending payments based on their calculated per-period payments

** When payment is soon
Alert user about the payment, decrease balance (transfer money from) and start saving for next
payment instance based on schedule.

** List payments
Show pending payments with up-to-date savings and total balance.

** Delete pending payment
Show saved amount for this payment to remove from saving account. Income period requirements descreased.

* Example
Now it's 17th of April. I set up salary schedule on 5th and 20th of each month. Then add new
recurring payment on 16th of April each year for 9000rub. This means we have 24 periods to save
9000rub, meaning that we have to save 375rub per salary.