Live demo in the browser

Thought it would be cool to be able to demo bitcore live from the browser. This creates one very simple bitcore example that people can edit and execute live from the bitcore.io website. Probably what we should do next is update all the examples to use the live demo ability (at least those that can run from the browser). Also, I just the default style for the codemirror editor, but we could also update the style with something that matches the bitcore style a little better.