add info on how much of tax paid at source can be deducted in polish tax form PIT-38

[jczaja]

If we paid abroud tax from dividends of higher value than 15% e.g. 26% or 30% , and due to agreement of avoiding dual taxation we should have paid only 15% then we can only deduct in PIT-38 15% , not 30%. So program should also print information how much tax we can actually deduct next to value of already paid tax