Mentoring: Display the position in the track of an exercise

It's been discussed before that Mentors should know at what position in the track an exercise is. But, I couldn't find an issue, so here it is.

Core Exercises are listed in the Track Order on the Mentor Queue Overview. However, that information is not available once a mentor starts mentoring. Or when they enter mentoring from a Notification.
For Side Exercises, the position is very hard to find.

AFAIK the decision that the Track Position should be visible in the mentoring view has been made. Could we make this high priority?

( @ihid )