Add new functionality to backend

• Introduce GUI for AK slide generation (#152 (closed))
• Add new admin actions for constraint violations (#154 (closed))
• Add admin actions to AK to reset interest and interest counter (#153 (closed))
• Implement generic views to reduce copy-paste for multiple preview/confirmation requiring admin actions
• Improve actions to publish/unpublish the plan (use intermediate/confirmation page, link on detail and status pages) (#159 (closed))