triggerMethod should support a space-delimited list of events

[paulfalgout]

If we want to replace trigger with triggerMethod https://github.com/marionettejs/backbone.marionette/issues/2508 ...

it will really need to support the same API.

this.trigger('foo bar') will trigger both foo and bar

this.triggerMethod('foo bar') will not call both onFoo and onBar