Resource based stubs

This is a follow up to #1248 (which I should've marked as WIP/proposal):
* The API-stub generator now works resource-based, so `ember generate api-stub someResource` will create `server/routes/some-resource.js` which has 5 express routes in it (get many, post, get single, put, delete). 
* Stubs routes are prefixed with `/api` by default