Changed TabControl to use ItemsSource Take #2

Initial set of changes to convert the current CefSharp.Wpf.Example to a Tabbed Control with ItemsSource.
Second take at this set of changes, this is the basic set to start with.

View -> ViewModel mapping is now handled by DataTemplate
Imported TabControlEx control to prevent tabs from being reloaded each time they've viewed
Added close button to each tab
Added some basic styling to TabItems
Add ViewSource command directly to WebView and IWpfWebBrowser
Added ctrl->t key cord to open new browser tab
Added ctrl->w key cord to close current browser tab
Added copyright disclaimer to header of each code file