DataGrid Fixes/Changes

[punker76]

• Closes Hotfix DataGrid row conditional foreground #1939 Hotfix DataGrid row conditional foreground. thx to @spaccabit
• Closes DataGrid Row Selection Color Lost #1876 DataGrid Row Selection Color Lost
• Closes Overriding DataGridRow Style #1492 Overriding DataGridRow Style
• Closes Any elegant way to override the style of Control, specifically, the DataGridRow? #1243 Any elegant way to override the style of Control, specifically, the DataGridRow?
• Closes How to Change the Accent for a Custom Control #809 How to Change the Accent for a Custom Control
• Closes Bug with DataGridNumericUpDownColumn #1878 Bug with DataGridNumericUpDownColumn
• Closes Datagrid ValidationRule issue #1930 Datagrid ValidationRule issue
• improve color styling, so overriding the colors is now easier than before

    <!-- DataGrid brushes -->
    <SolidColorBrush x:Key="MetroDataGrid.HighlightBrush" Color="{StaticResource AccentColor}" options:Freeze="True" />
    <SolidColorBrush x:Key="MetroDataGrid.DisabledHighlightBrush" Color="{StaticResource Gray7}" options:Freeze="True" />
    <SolidColorBrush x:Key="MetroDataGrid.HighlightTextBrush" Color="{StaticResource IdealForegroundColor}" options:Freeze="True" />
    <SolidColorBrush x:Key="MetroDataGrid.MouseOverHighlightBrush" Color="{StaticResource AccentColor3}" options:Freeze="True" />
    <SolidColorBrush x:Key="MetroDataGrid.FocusBorderBrush" Color="{StaticResource AccentColor}" options:Freeze="True" />
    <SolidColorBrush x:Key="MetroDataGrid.InactiveSelectionHighlightBrush" Color="{StaticResource AccentColor2}" options:Freeze="True" />
    <SolidColorBrush x:Key="MetroDataGrid.InactiveSelectionHighlightTextBrush" Color="{StaticResource IdealForegroundColor}" options:Freeze="True" />

• new attached dependency DisabledVisualElementVisibility for TextBox, PasswordBox, RichTextBox and NumericUpDown, makes it easier to hide this element if we don't want/need it

Before

After