Integrated ember-simple-auth into addon

This should resolve #16.

Everything is now moved into ember-gdrive.

One last thing I was hoping we'd avoid but ended up being necessary is accessing the containing application's config from within the addon.

The reason for this is that we need access to the GOOGLE_CLIENT_ID parameter. I'm currently looking into the best way for us to achieve this.

I believe doing it via an initializer is possible.