fix #586 System.Windows.Data Error: 4 with Glow

fixes for

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='MahApps.Metro.Controls.Glow', AncestorLevel='1''. BindingExpression:Path=GlowColor; DataItem=null; target element is 'SolidColorBrush' (HashCode=34418569); target property is 'Color' (type 'Color')

Closes #586