triggerMethodOn

stuff:
+ adds triggerMethodOn
+ cleans up region code with triggerMethodOn
+ removes triggerMethod closure because, why not...

So, i'm -1 for this because I would prefer to use Class methods where they're helpful than add methods to the prototype. `Marionette.triggerMethodOn` doesn't take advantage of `this` so adding it to the prototype is just a style thing. 

@marionettejs/marionette-core ?