Add first pass at Ember guidelines

These are the first few things I've seen that are consistently useful. All feedback and input is appreciated.

cc: @jsteiner @BlakeWilliams @seanpdoyle @halogenandtoast @creuter @MattMSumner @JoelQ 
I don't the controller should ever care or know how it's properties are being used which is one reason I'm okay with handling save, rollback, etc. at the controller level.