ember-cli addon

I am publishing the PR so there could be more eyes on it. It is not ready to merge.

- [ ] cleanup generated files
- [ ] complete the README with new instructions
- [ ] make sure I did not make some stuff worse in the process of refactoring :)
- [ ] add some basic tests

Mainly I would like some feedback on how I manage configuration. Is it too much magic?
and more in relation with this PR. `setup` is meant to be called outside of `init`. In case you do not provide `url` param on the adapter and want to configure it later. Or even change the database on runtime.