Update to serve as Ember CLI Addon.

* Add Ember CLI addon.
* Add grunt copy task to prepare vendor/ subdirectory for publishing to NPM.
* Adds `ember-cli-addon` keyword (and `firebase`).

You will need to publish to NPM, but then once 0.0.35 is published users can simply run `npm install --save-dev emberfire`, and it **just works**.

Closes #75.
vendor/ is where ember-cli expects bower_components to be. With this PR, the firebase.js and emberfire.js files (for npm packages only) are in vendor/. But dist/ is still checked in for bower consumers. 

The way that the final vendor/ builds are done in ember-cli is that all addons can merge their code with the vendor/ dir, and the applications vendor/ dir wins any conflicts. So the reason we want to use vendor/ is so that ember-cli consumers/users can simply add emberfire to their bower.json files to override the vendored version in the NPM package.