Implement action factory

[logmanoriginal]

This PR is about reducing the size of index.php by moving actions into separate classes and making them available via an ActionFactory. That way additional actions can be added and tested without touching existing ones. The behavior is similar to bridges, formats and caches.

Tasks

• Link actions in a factory class instead of using a case structure
• Implement a base class for factory classes (partially done)
• Add separate classes for each action
  • Display
  • List
  • Detect
• Add tests
• Add documentation
• Code cleanup
• Testing

References #1001

Let me know if you have further suggestions for improvements.