only style formatting
fix background for MetroCircleButtonStyle
add MetroCircleButtonFocusVisual

fix also IsMouseOver and IsPressed for MetroCircleButtonStyle and
MetroCircleToggleButtonStyle (should only be triggered if mouse is over
ellipse)
fix foreground theme usage
use BorderThickness as StrokeThickness
remove unnecessary border from focu visual style
fade out effect on IsPressed
fade out effect MetroCircleToggleButtonStyle

 too
Merge pull request #672 from MahApps/punker76-MetroCircleButtonStyle-issues

fix some metro circle button style issues