Provide extension points to LiveReload plugin

We should refactor the current LiveReload core plugin by providing one or more extension points that would allow other plugins to:

• create / start / stop the LR server
• provide with the javascript file to inject (livereload.js or custom js file for AngularJS tooling, for example)
• get access to the websocket connection that has been established with the browser if the js file it loaded opened such a connection