Allow adding descriptions for file and directory fields.
- This is useful when a file or directory field is dependent on some
  condition.
- Using a description means when you hide a file or directory field its
  related text is also hidden
Allow adding description for radio fields.
- This is useful when radio field is dependent on some condition
- This way related text will hide if radio buttons are hidden
Merge pull request #218 from mtjandra/IZPACK-1119

[IZPACK-1119]