EAK Migration Guide Update

This PR will update the EAK migration guide and sync it with the latest revision of ember-cli. How's next Monday sound for a deadline? Following is a list of updates that should be added, shout out any fixes/revisons/etc and I'll get them up ASAP, I'm just catching up too.

[ ] Should now use import Ember from 'ember' and import DS from 'ember-data'
[ ] Migrating the API Stub
[ ] Customizing the Express Server
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