Add a course "test mode" for teachers and admins

Problem/Motivation

Currently the only way to test a course is to actually take it. The problem with it is that teachers / admins don't want to have results included, also, if lessons have randomization and random activities enabled, not all activities can be visible when taking the course the standard way. We also don't need to store results when a teacher / admin is just testing.

Proposed resolution

Create a test mode for teacher / admin users:

• Additional controller method without any free navigation access checks,
• All activities displayed at a default order (lesson randomization not effective),
• Answers, lesson status and course status not created / saved
• Current lesson and activity stored in user session.

For that purpose we can create a base class for the answering form and extend it in the actual answering form with all the answer and status save logic that's already in place and create a second extending class for test answer form without it and with session handling of current activity and lesson.