Adding "By" method aliases

This PR is to add "By" method aliases to many methods in Ember Enumerables.  

I've worked through one example of adding aliases to Enumerable mixin. I'd like feedback on how these additions should be tested. 

Currently, I am passing both method names to a utility function that just runs the test twice, once with each name.  I can't tell if wrapping every test in something like this is the correct amount of coverage, or overkill.