Comments UX + Notifications Revamp: Group / Username mentions (with autocompletion) feature should be a hard dependency built-in to the core, not a plugin

"@" mentions (of individual users, or user groups) is a standard workflow in every modern collaborative web platform that has commenting, reviewing, multi-user editing, etc.

If we want to create a good UX that "works" for Comments UX + Notifications revamp, we should be able to depend on this functionality being there; not a plugin, not an option.

So let's make @ mentions a hard "core" dependency within Tiki, so that it can be consistently used for:

• Tiki tracker fields and descriptions
• Comments
• Wiki page contents (and history)
• Forums
• Anything else that cites users or history, or anything else involving notifications and assignments