Create E2E tests for CKEditor

Create/maintain the tests both for Visual Editing and to guard against regressions in the Content perspective.

For testing, use the wrapper created/adjusted in RD-3677.

Functionality which should be covered by ui tests in scope of PSP2:

1. Link piker. - Done
2. Image piker.Done
3. HTML cleaning. Done
4. Text formatting. Done
5. Required validation.
6. Formated fields