Fix for a severe Date parsing error with Culture de_AT (German / Austria): Any Date in Month 'March' was not parsed correctly in Method 'LongDateStringToDateTimeInternal', which is a very central Method in OpenPetra.!

This fixes 77 (!) Exceptions in the NUnit Test 'TestOpenAllWindows_de_AT' when run in March...!

I also added a new NUnit Test, 'TestOpenAllWindows_de_CH' (German / Switzerland), for good measure...