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 often use `save` and `destroyRecord` outside of the route because it makes sense when it's tied to actions. I was thinking methods like `find`, `findAll`, etc. So maybe avoid calling finder methods outside of routes?