Update testing guide

[harryadel]

• Update test data and publications section with code examples on how to do things manually without the use of packages.
• Add a 'testing-methods` section.
• Replace Chimp references with Cypress.
• Update code examples by removing references to Meteor's underscore & jQuery.
• Replace faker reference with the new fork.

We might also need to un-archive the official todo example and update it but I guess that's for another day.

[StorytellerCZ]

Great update!

[filipenevola]

Looks great. Thank you.