Message refactor fixups

Done

• Handle unread messages marker properly
  • implement another API endpoint to mark messages read. Messages are now marked read on:
    • Retrieving a single conversation
    • Retrieving the first messages for a conversation
    • Calling the mark as read endpoint
• Fix some weird loading behaviour for the full page message view. (It loaded all conversations for the opened chat windows - overwriting each other with a bit undefined behaviour which one stayed in the end)
• Fix profile images in topbar messages view as well as full page messages view
• Add old message format to websocket messages so production will also understand them
• Handle old message format from websocket so we will show something from there. We might do double-HTML encoding on display here, but I don't care.

ToDo

• fix push notifications