Changed style of DataGridNumericUpDownColumn when Column has IsReadOnly=true.
The new behaviour is, that instead of IsEnabled, IsHitTestVisibile is set to false.
Now in a DG-NUD-C the Background of the column is transparent in DefaultElementStyle
[NUD] Padding property in NumericUpDown is now used
Merge pull request #1335 from xxMUROxx/hotfix/MetroDataGridCheckBox

Changed style of DataGridNumericUpDownColumn