handle RightToLeft for check path
introduce ContentDirection attached property
example
Merge pull request #1100 from MahApps/1084-punker76-CheckBox-RightToLeft-Style

RightToLeft for CheckBox/RadioButton and Style for Content on left side (without setting RightToLeft)
doesn't set TextBlock style and foreground
introduce MetroPage style
Merge pull request #1102 from MahApps/1094-punker76-textblock-foreground

doesn't set TextBlock style and foreground