Upgrade package & add demo app

[elwayman02]

This PR does the following:

1. updates the addon to the latest dependencies via ember init
2. Adds a demo app and deploys it via ember-cli-github-pages

An example of the deployed demo can be found here: http://github.jhawk.co/ember-world-flags/

You can deploy it for your own repo using the EmberUp tutorial (skipping the first command, since I've already installed the addon to the project).

Note: The gh-pages build produced by ember-cli-github-pages has a bug with public asset locations. To fix that, simply edit the vendor CSS files as follows:

/ember-world-flags/images/flags16-[fingerprint].png
becomes
/ember-world-flags/ember-world-flags/images/flags16-[fingerprint].png

and the same for the flags32 file. This will give gh-pages the correct path to find the files when they are deployed.

More info on that bug can be found here: poetic/ember-cli-github-pages#11

[rounders]

@elwayman02 thanks for the pull request 👍 I'll have a look through it this evening.

[rounders]

merged, looks great @elwayman02, thank you!!