Consider integrating Appitools

[morrinene]

Applitools offers a cloud-hosted visual regression testing platform. It's a commercial service. I'd like to add support for it (beyond our free visual regression testing suite) as a way for 1) more people to use Intern 2) another service we can offer our customers 3) marketing (Applitools is interested in co-blogging/promotion/webinar, etc.).

They have 3 ways to integrate, the most interesting of which would be to create another DigDug Tunnel and then use their subset of the WebDriver API to make calls. They have some interesting features, such as full page screenshots, cropping part of a page, etc.

Adding this here for consideration in a subsequent version of Intern 4.