False template option for ItemView

This is the general idea after reviewing #1042, abstracting template rendering logic to renderTemplate and stopping its execution if the template is false. This may need more tests, but it currently mimics the base rendering spec as well as verifying no error is thrown in render.

One concern is that the error thrown in Renderer when the template is falsely mentions false as an incorrect value. This is not the case for ItemView with this PR, so this will be a misleading error. I've added an error to ItemView#renderTemplate at the moment with an appropriate message and updated specs accordingly.

I had to change one test in the Renderer spec, but I'm not sure if this will be intended behavior when overriding Renderer.render.
 don't think you need the trigger spies as that's really covered by triggerMethod. @marionettejs/marionette-core thoughts?