Element manager spike

So, moving away from the inheritance model, I came up with an `ElementManager`. It feels pretty good, and should be easy to use from JS as well as coffee. 

@nathansobo, would love a review + ideas. It's obviously a WIP as things will need to move around. Just trying to get a handle on what feels good for the general API.
This is the worst part IMO. It is explicit and I suppose it lets you opt out of the whole template thing if you want, but feels a little dirty. Would be nice to have this be a little more automatic?