[x] Updates the documentation about onboarding and step objects properties + updates the diagram for a ditaa diagram instead of a photo
[x] Splits tests in two files: one for the onboarding class and another for the step class
[x] Adds missing tests for onboarding and test objects
[x] Adds a script in package.json to watch client tests (the tests listen changes and run again each time a change is detected): npm run test:client:watch
This PR:
npm run test:client:watch