Add a demo page ready to deploy to GH pages

[WillEngler]

WIP to close #45.

Important changes:

• Dummy app is clickable demo
• Uses ember-cli-github-pages addon to make building and deploying dummy app to gh-pages branch straightforward with ember github-pages:commit --message "gh-pages branch commit message". See example at willengler.com/ember-cli-flash/
• Points integration tests to new /test route so that you can edit the index route to your heart's content without worrying about messing up the integration tests
• Adds Bootstrap button styles to dummy app CSS

Blocking issue:

If you check out my example example (ha) you'll notice that the messages never disappear. When I do a fresh clone, install, and ember serve of poteto/ember-cli-flash I see similar behavior on the existing test app. The existing dummy app does not explicitly set a timeout, so the timeout should be 3000 ms. But when I run the original dummy app, the messages hang around indefinitely. Do others see this behavior on a fresh install? It seems implausible that I'd be the first to notice a bug preventing timeouts from working, but I don't know where to start looking for the problem in the dummy app.

[WillEngler]

Just now seeing 49d2d593ed7a431420f8632f057c0c681ec023bc. So the groundwork had been laid for this a while back.