fixed wrong changes from commit a0c999effe1df8668047bc1a3159d95c8ebc2db3 "fixed Clang warnings"
Better handling of offers with exchange rate:
* exchange rate is now saved after closing window
* additional column for price in euros on printout when offer is in PLN
* one function for handling enabling/disabling exchange rate
Rearanged column order and width on printout + refactored consts for column width
Fixed saving/printing offer without client