Add triggers support to behaviors

I started looking into #1642 because I recently needed the functionality.  This was my initial attempt to implement triggers for behaviors without duplicating too much code.  At first glance, this should be BC.  It still needs more specs and the first `calledWith` needs fixed.  I still need to match the expected `args` parameter, but I'm getting max call size.

Need lots of eyes and feedback on this one because behaviors are still relatively new to me too.  It's semi-modeled after the implementation for `behaviorEvents`.

Note this is also introduces `Marionette.buildViewTrigger` and `Marionette.proxyBuildViewTrigger` to avoid code duplication from `View#configureTriggers`, so I'm not sure how we feel about that.
I'd like to see that too, but any changes we make should be made to Events as well and that seems like a separate refactor task. I like keeping this code as similar to behaviorEvents as possible, for the moment. 

The other thing - is it'd be nice to move some of this to a Behavior method. Logic in a behaviors object literal seems really ugly to me.