Follow cypress best practices for Selecting Elements in example app: website/cypress

The [Cypress Best Practices](https://docs.cypress.io/guides/references/best-practices.html#Selecting-Elements) recommends usage of embedding `data*` attributes to isolate from CSS and JS changes.

The example app currently uses [CSS selectors](https://github.com/hoverinc/picklejs/blob/master/website/cypress/support/step_definitions/home/selectors.json) 