Add OnGotFocus and OnSetFocus
Add CefFocusSource enum for mapping from cef_focus_source_t enum
Add license disclaimer
Fix return type and minor formatting
Move Focus methods from IWebBrowserInternal to IWinFormsWebBrowser and only call them in the context of the WinForms ChromiumWebBrowser
Pulling in amaitland:CefSharp feature/focus-handler changes