Add bower.json

cf: #65 
cc: @jamesarosen @shajith 

Before we register a package with Bower we need to think about **where the built and released version of Ember Resource should live**. We do not have a built copy of Ember Resource checked into this repository.

We do have a built and released copy that lives on cdnjs, we advertise and link to this copy in the [Readme](https://github.com/zendesk/ember-resource/blob/master/README.md#ember-resource).

---

Bower expects a repository with a list of tags in it, scans the `master` branch, and takes **all of the files** in the registered repository. If we use this repository, we would end up ignoring our build tools, tests, and unrelated files (e.g. `package.json` for `npm`).

Ember and Handlebars solve this problem by creating a brand new repository that only contains the files built for distribution -- https://github.com/components/handlebars.js and https://github.com/components/ember respectively.

---

So, we have a few options:

1. Create https://github.com/zendesk/ember-resource-bower
2. Attempt to get into https://github.com/components/ember-resource
3. Check in a built copy of Ember Resource to this repository, and instruct Bower ignore all other files.
4. ??