triggerMethodOn

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

I interpreted this as adding `triggerMethod: Marionette.triggerMethod` to the `Region` prototype, not creating a proxy method `Marionette.proxyTriggerMethodOn`.  I think it looks nicer to call `this.triggerMethodOn` inside a core class and be consistent with other Marionette functions used inside core classes.