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.
Support toolbar
Add appropriate icons
Update MahApps.Metro/Styles/Controls.ContextMenu.xaml

Added the resource brush used in the version which has been pulled into the main branch.
updated ignore file to include packages
cleanup code behind files in sample
fixed compiler warning by including RaisePropertyChanged code in default tile implementation
code rules updated - private fields are prefixed with _
removing dead code and confirming a private fields is no longer used
removing more dead code
removed unused property
compiler warning - _isDragging is never assigned
cleanup demo to use PropertyChanged
removed some whitespace
added RecognizesAccessKey value to CheckBox style, fixes #311