Use builds.emberjs.com for ember dependency in bower.json.

As discussed in a few issues (most recently in #55) we depend on the components/ember repo for the bower dependency resolution.  This PR changes our bower config to use the http://builds.emberjs.com/ system so that we don't need to use another repo for this.  

Since both this PR and #59 modify `bower.json` and a few of the `index.html` files one will need to be updated before merging.