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 
What's the benefit over just doing it in the controller where the action is hit? I can think of a lot of times where I need to set other properties and do other things THEN save, just call another event?