Feat(full) Setup cypress for e2e (#67)

• Setup and configure cypress for e2e testing
• Add e2e testings for:
  1. Login with feide
  2. Create/delete course
  3. Create/edit/delete unit
  4. Submit/decline reflection
  5. Generate/download report
  6. Invite/enroll users
• Add cypress.env.json.template for setting environment variables for testing
• Add necessary id's to components for testing purposes

How to test:

1. Makes sure the database is wiped, and then run both backend and frontend
2. Go to frontend folder
3. Add necessary info to cypress.env.json file
4. Run "npx cypress run" to run the tests in terminal
5. Run "npx cypress open" to run each test in browser
6. If the tests fail make sure you delete the database and restart backend before running again

Closes #67 (closed)