Integrate visual regression testing

[chandlerprall]

This issue is meant to track implementing the visual regression testing that @silne30 added in #630.

• wdio-visual-regression-service dependency must be built (currently pulls from source and not building it)
• document Best Practices and expectations for writing these tests (Add guide to writing visual regression tests to README.md #677)
• integrate with CI

[cuff-links]

There is an infrastructure issue open for the integration with CI point. Can't leave the link here for privacy concerns.

[cuff-links]

We are also waiting on the PR for wdio-visual-regression-service to be merged into master on it's source repo so it gets built automatically. Still waiting for the thumbs up on the review.

[cuff-links]

Still waiting on that PR. I have been following up with the maintainers and haven't really gotten much response.

[chandlerprall]

Closing this issue - without someone championing it, a lack of [known, perhaps] regressions to justify visual regression testing, and the additional work required to solidify the previously-agreed upon approach, we don't feel the need to implement.