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
Fix Indentation

Fix indentation from previous commit (change from tabs to spaces)
Remove commented out code
Remove call to Cef.Initialize() in OnZoomLevelChanged
Merge pull request #306 from amaitland/master

WPF ZoomIn/Out Functionality