Improvement: Add activity completion info for teachers in course index

[AntonT76]

Hello,
an improvement for the course index—perhaps this could be possible to implemented it in Boost Union.

Is your feature request / improvement related to a problem? Please describe.
as a student I can see the activity completion in the course index (circle/green circle). But as a teacher I have to open "Reports - Activity Completion" to see which activities provides an activity completion.

Describe the solution you'd like
It would be nice for teachers if there is also an admin option (activate/deactivate) in the Boost Union Backend to place an activity-symbol in the course index - similar and near to the "door lock symbol" to hidden activities in the course index.

thanks & best regards
Anton