Screenshotting support

I have added API for creating screenshots and for changing the viewpoint resolution.  The API from Mocha to PhantomJS is achieved using specific console.log's that PhantomJS listens to.  I have tested this and working well.
I still feel like I'd want to define the pattern along with other grunt configuration, rather than application-level code. But, that's just splitting hairs when there's a working solution here.