The user would be notified if the message contains "@" followed by the user's nickname or forum username. An alert would be shown, and the icon and message in the status bar would be changed. All notification is only shown if the chat window currently does not have focus.
Also added a connected_notification icon for showing in the status bar.
Displayed username along with nickname (when they are not identical); Requested and displayed user's avatar; Made the dialog bigger for extended names.
Added a few functions to web_backend (GetImage, GetPlain) to support getting data in multiple content-types.
Added a no_avatar icon for users without avatars.
In dark theme, it is very hard to see the connected/disconnected icons because they are dark too. So I added two white-coloured icons for the dark theme. This also fixed an issue where theme update does not change the icon on the status bar.
