Add Stop to IWebBrowser and implement in WPF WebView
Add StopCommand to WPF WebView

Conflicts:
	CefSharp.Wpf/WebView.cs
Improve IWpfWebBrowser comments (add missing punctuation and make other comments consistent).
Improve XML comments in IWebBrowser
Re-Add StopCommand (rebased this PR on latest master, had a slight merge issue, so manually re-adding change)
Merge pull request #358 from amaitland/feature/browser-stop

Add Stop to WPF WebView