Group/team/user progress (matrix) page: add more infos in popover

[smadbe]

Overview

The current services do send us much more information than what we display in the stats matrix (while observing). First, let's display these info in the "popover".

Acceptance criteria

• add ":" between "Time spent" and the value as they are close

Between time spent and the score, display:

• bulb icon "hints requested": ...
• "latest activity" and the date in a very short format: either "x min ago", "x hours ago" or the date (with hours) if older than a few days... hovering should show the full date (the same as we did in the forum? if not, it should probably be a separated PR)
• # submissions
• "started" and the date (same as above)
• don't display "latest_activity_at" and "started_at" rows if null
• on group progress for groups: add "avg" in front of "time spent", "submission", "hints requested"
• on group progress for groups: add "validation rate" with the value as a percentage, e.g. "22%"