Update testing section with Cypress

[StorytellerCZ]

We should update the testing section by removing old ways of testing with Chimp, etc. with Cypress as per recent blog post: https://blog.meteor.com/testing-a-meteor-app-with-cypress-bfb3d3c6ed6f

Also the entire testing section could use an update.

[kakadais]

So the default testing tool would be changed to Cypress? Good post and Great job-

[StorytellerCZ]

For E2E tests it would be Cypress.