Implemented OnStatusMessage and event for WPF and WinForms for CefSharp1

We're using CefSharp1 because CefSharp3 is quite unstable for us. I've implemented `OnStatusMessage` and a `StatusMessage` event for both the WPF and WinForms `WebView` controls.

A couple of things I wasn't sure about:

1. The naming/placement of the `StatusType` enum. I've been consistent with .NET conventions and kept it in its own file. Other declared enums went with their handler, but this patch doesn't have an associated handler class.

2. Are we OK with just using the event handler (similar to how `OnConsoleMessage` is done)?

PS - I plan to re-do this PR for CefSharp3.