Allow to edit prompts with ckeditor instead of plain text

Problem/Motivation

CKEditor would allow to bold text and similar for good visual looks.

Steps to reproduce

Proposed resolution

Final prompt output should be in markdown.

Options to achieve it:
1) Convert HTML to markdown on save and convert back to HTML on display.
2) Save HTML, and convert HTML to markdown on generating output.

Remaining tasks

User interface changes

API changes

Data model changes