[UI] friends can @ friends who havent posted in a discussion #1950

Requirements

• [X] This is a feature request and not a bug report. Otherwise, please create a new bug report instead.
• [X] Please check to see if this request (or a similar one) already exists.
• [X] It's a single feature. Please don't request multiple features in one issue.

Describe the feature you'd like

"@mrsmellypants check this out" "@friendsonline look at this" "@friends cool info"

you get the gist, comment is invisible to everyone else as not to clutter