Extension updater: allow to check old results without needing to check again updates

In Aministrations > Extension > Updater, it's apparently not possible to display again the results after performing a "Check update".
It should be better for performance to not have to check updates every time, but to be able to get older results computed (especially if the check was performed 5 min ago), and to have the possibility to refresh those results with a new check if needed.