Introduce "separator" prompt segment

Problem/Motivation

"Separator" could differentiate between different prompt segments, indicating beginning and the end of the section.
This might be useful to indicate for AI where what sections begins and ends.

Steps to reproduce

Proposed resolution

1. Create "separator" prompt segment.
2. Provide predefined separators like
   • -------------------------------------
   • ******* section name ***** (with name of section)
   • [other, research what separators might be best]
   • [custom]
3. Allow to enter name of the section
4. Maybe show real time preview with javascript how the separator will look like (combining separator and section title)

Remaining tasks

User interface changes

API changes

Data model changes