Add integration mode to html reporter

When adding tests to an existing page, we want mocha to be unobtrusive. Adding the css class `integration` to the mocha div will enable the integration mode of the html reporter. This will:

* Remove the report from the page flow, and hide it by default.
* Add a toggle to the stats panel to show/hide the report.
* Modifies the css to remove some built in assumptions, where the report styles would be inherited from the base page. (and thus unreadable if it is loaded in a page with a white on dark color scheme, for example).
* Add the css class `bottom` to the mocha div, and the stats panel will move to the bottom of the page.
* Adds a test to demonstrate its usage. Run: `node test/browser-integration/index.js`, and visit `http://localhost:3333/`

With this, we can write integration tests for our single page app with mocha.