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.
Thanks for looking this over, @jasonLaster. More sets of eyes on something like this is great. I may have went a little overboard when abstracting each method, so it may not be entirely straightforward.  I know we originally wanted to refactor the way `behaviorEvents` are built because a lot of the same code was repeated to make triggers happen.  I can reevaluate `BehaviorEventsBuilder` to see if it can become less ambiguous.  I'd like to hear the others feedback as well.