Update MahApps.Metro/Styles/Controls.ContextMenu.xaml

When a sub menu is popped-up, it's foreground colour would follow the parent. Since the parent's foreground is white, its foreground is also white. The update force the foreground colour the dirty way.
Update MahApps.Metro/Styles/Controls.ContextMenu.xaml

Added the resource brush used in the version which has been pulled into the main branch.
Merge branch 'patch-3' of github.com:programatix/MahApps.Metro into programatix-patch-3
updated ignore file to include packages