New: Graphical CPDatePicker clicking on the arrows with key mask Command/Control/Alternate

Now when clicking on the arrows with the key mask Command/Control or Alternate change the date to 1 year or 10 years as in Cocoa.
Merge pull request #2083 from Dogild/CPDatePickerAltCommandButton

New: Graphical CPDatePicker clicking on the arrows with key mask Command/Control/Alternate