Some improvements for Chat Markers:
- Use double-check icon for displayed messages (for accessibility, this is better than displaying the check mark in a different color)
- store 'displayed' markers in the chat archive DB
- fix the database entry conversion for querying markers
- show 'displayed' markers when restoring a conversation
- send Chat Markers when actively following a conversation (window has focus, is scrolled to the bottom, etc.)
Note that I created
feather-check-symbolic myself, so it is no official Feather icon.