RFC: add an instantReplay feature (built-in data mocking)

Sometimes when working with dynamic content, hiding and deleting selectors isn't enough. If we really want to test our CSS changes proper we need to use the same DOM data. Unfortunately -- it's not always easy to mock data -- especially if we are testing a production site...

I would like to propose that the `gulp reference` flow _also_ capture actual DOM selector data _and_ (as an option) re-injected that data when running `gulp test`

Comments welcome!

_see implementation ideas in the "instantReplay" branch_

Start by reviewing the instantReplay branch and the gulp reference and gulp test flows mentioned in the issue. Determine how actual DOM selector data would be captured and optionally re-injected. Done means reference records the data and test can use it when the option is enabled.

Written by the indexing model from the issue text.