Improve layout and strings for network experiments

We added three strings related to network experiments to our status-site repo:

Ongoing
None
This experiment is still ongoing

I recall @arma not being happy with "Ongoing" on our landing page in case an experiment is currently happening. I think Active was supposed to be better. I am not sure whether we want to have None for the case no experiment is currently running. The same goes for This experiment is still ongoing which is shown if the user is clicking on Network Experiments and the experiment is still running. Tagging some UX folks, too, in case they have an opinion. /cc @arma @duncan