WPF ZoomIn/Out Functionality

Added GetZoomLevel and SetZoomLevel methods to ManagedCefBrowserAdapater
Currently unable to get GetZoomLevel to return any value other than 0,
comment in source says "This method can only be called on the UI
thread", so need to investigate that further. SetZoomLevel works as
expected.
Added WPF Commands for ZoomIn, ZoomOut and ZoomReset.
Added Dependency properties for ZoomLevel and ZoomLevelIncrement
Added content menu items for ZoomIn, ZoomOut and ZoomReset to Wpf
Example