Use example component partial as code example and screenshotable component

[bensheldon]

• Renders out the file contents of the component's example partial (living under views/cfa/styleguide/examples) for the styleguide's code example. This makes the documentation closer to how component would be used in ERB, and allows more complex (e.g. multiline or components that use yield or capture) examples.

• Creates a URL path for each component example. This could be used as a target for Happo as described in Set up CI #4. Example: http://localhost:3000/cfa/styleguide/examples/molecules/progress_step_bar

• I extracted out the styleguide section into a separate partial too. I still see some complexity/potential-confusion in differentiating when a full partial path is being passed as an argument versus a component "identifier" that is then expanded into a full partial path.

[bensheldon]

Pattern has been superseded.