Color and Accent Cleanups

-) Added AccentBrushes for all Accents and replaced where possible
(needed) in controls
-) Renamed BraindingBrush to ProgressBrush and changed gradient to
HighlightColor -> AccentColor3
-) Renamed HighlightDarkColor to HighlightColor (because they where
always the same and only HighlightDarkColor was used)
-) Commented unused Brushes out (HighlightLightBrush,
NavigationBorderBrush, NavigationForegroundBrush, PageBorderBrush,
BodyTextColorBrush, HoverHyperlinkForegroundBrush,
HoverHyperlinkBackgroundBrush, ItemSelectedBrush, SliderTrackBrush)
Brush Cleanups

-) Exchanged Colors with Brushes where possible
-) Use WhiteBrush and BlackBrush instead of WhiteColorBrush and
BlackColorBrush everywhere (majority already used it that way)
Removed AppBarButton, renamed colour to color

-) Removed AppBarButton.cs and .xaml
-) Renamed Colours.xaml to Color.xaml
-) Renamed all occurrences of colour to Color
Changed gray tones order
Merge pull request #3 from MahApps/master

Merge MahApps master
Merged Master
style formatting
use brush instead color to fix issue #586
Merge pull request #706 from MahApps/586-punker76-glow-error

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