Add DOM selectors to assist with Cypress tests

[pjmonks]

Following best practices for the new Cypress end-to-end tests, as described here: https://docs.cypress.io/guides/references/best-practices#Selecting-Elements

Updated a number of existing views (with some refactoring) to add data-cy attributes to various DOM elements. This allows Cypress tests to precisely locate DOM elements required for testing, without having to assume CSS classes, intrusive ids, etc.

This covers the following page views:

• Data Models
• Terminologies
• Code Sets
• Reference Data Models
• Folders

Also refactored some common functionality to shared components to avoid repetition.