[TESTING] Refactor cypress tests

[jpelay]

As stated by @rix0rrr in #3972 there are two ways in which our tests can be improved:

1. Test organization: Instead of having defines with a single it we can group different tests under a single define. Saving code and making our test suite more organized.
2. Selecting HTML elements by ID: Cypress actually prevents against using id or other HTML attributes used in functionality for the tests.

Update: I will change tests bit by bit

• [x] admin page
• [x] explore program page
• [x] feedback -> #5393
• [x] for-teacher page
  • [x] class page -> https://github.com/hedyorg/hedy/pull/5530
  • [x] customize class
  • [x] customize adventure -> https://github.com/hedyorg/hedy/pull/5683
  • [x] general -> #5592
• [x] hedy page -> https://github.com/hedyorg/hedy/pull/5648
• [x] home page
• [x] login page
• [x] recover page
• [x] signup page
• [x] subscribe page -> #5647
• [x] lezer test
• [x] public adventures
• [x] public programs
• [x] teacher page
• [x] tools -> https://github.com/hedyorg/hedy/pull/5683

[Felienne]

One more task for @Annelein?