Upgrade to latest Django CMS

[pdelboca]

Our site needs a little bit of love since it is running in really old versions of Django CMS.

There is a long road from 3.x to 5.x with important changes at the schema level so we rather go slow and secure.

Tasks

• Upgrade Django CMS from 3.x to 4.x ([WIP] Update requirements to Djanco CMS 4.0 #1163)
• Cleanup unused Static Placeholders
• Cleanup search feature (Search returns a 500 error #893 Error 500 searching #1090)
• Upgrade Django CMS from 4.x to 5.x
• Upgrade Django version from 4.x to 5.x