Convert to Ember CLI addon.

Fixes #8. I've converted this into an Ember CLI addon. I've made it to where you can specify which orbit files you want included in your environment.js file. I've updated the README but it the install instructions won't fully work until my pull request is accepted. Further, the instructions will change when it goes on npm.
You should have some sort of check here to make sure `ORBIT.IMPORTS` exists and throw a usable error to the user when it doesn't.

Also, It should always have orbit.js and orbit-common.js, they can't opt to not include those since ember-orbit won't work without them.

It could be simplified to something like:

```
orbit: {
  jsonapi: true/false,
  localStorage: true/false
}
```

The user won't know the file names since they are all container within the ember-orbit directory.