Adds #1088 - Creates properties to set column widths for BaseMetroDialog

This add the ability to set the width percentage for the BaseMetroDialog.
```
           var settings = new MetroDialogSettings
            {
                AffirmativeButtonText = "yes",
                NegativeButtonText = "no",
                FirstAuxiliaryButtonText = "cancel",
                DialogWidthPercentage = 70
            };
```
My application is only 460 wide and it was cutting off half of the first button when using three buttons at that width.  Adding this fixes that issue.