Tooltip to show @name when hovering over user info in discussions

When users participate in discussions it shows their thumbnail and full name but does not indicate their @name.

While we can find their @name by clicking on their thumbnail to visit their profile page this far from ideal in the middle of a comment when we're trying to @ tag someone.

Suggestion:

When mousing over a user's thumbnail or name show a tooltip with their @name. This will allow commenters to @ tag the correct user more easily.

This would be useful because:

1) until now (at least within Enspiral) we've tended to set up @firstlast usernames. As the user namespace gets more crowded we're going to hit multiple users with the same name across Loomio and within large groups.

Commenters may @tag the wrong person with the same First Last name within the current group, or get frustrated because they're trying to accidentally tag the wrong person and getting told the user isn't a member of the current group.

2) Some users don't always have their last name showing which also makes it more difficult to identify the person's correct @name in a discussion without clicking to view their profile.

3) Users can edit their profile to change their First Last name to something other than real name. This makes it very difficult to identify them by their @username without visiting their profile.