Ensure that the buttons that control the custom panels adhere to its on
enabling rule when the custom field is enabled. Otherwise you will be
able to remove rows when there is only one row.
Hide buttons if minRow and maxRow are the same value. In this case there
are no need for row controls.
Merge pull request #249 from mtjandra/IZPACK-1143

[IZPACK-1143] - Ensure custom field's cannot go below its defined minimum row