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 think you should let those actions bubble up to the route for that kind of situation.

This is one reason I wanted a rule in place, it seems that no one has drawn a clear line of where these make the most sense.