add window commands to flyout demo
introduce WindowButtonCommands
fix button height of WindowCommands
don't focus FlyoutsControl
don't focus MetroContentControl
introduce ShowWindowCommandsOnTop

! fix ZIndex if more than flyouts are open
! allow for flyout.Position == Position.Top too
add ShowWindowCommandsOnTop to flyouts example
some cosmetics to flyout demo
change header template if feature is on
PART_BackButton always at bottom
fix TextElement.Foreground

should be FlyoutWhiteBrush
Merge pull request #709 from MahApps/708-punker76-windowcommands-with-flyouts

extend feature windowcommands over flyouts #708