Add an option to compute tax data (revenue & cost, dividend/interest and paid tax) from given country

When doing taxes from foreign capital gains it is needed to submit pit-zg form for given per given country where taxable gains were recieved from. So it would be useful to add  some option like "--country" with possible values "us", "pl", "je", "ca" etc. so then computation is only made for income originating from selected country. This should help when to fill pit-zg (done per country)