Discovery of online events

Content should always be filtered according to the location.

One exception: online events.

Currently, one has to set online events to "Yes" then clear manually the location. Then when they want to see physical events again, they have to set online events to "No" then enter the location again.

Wished behavior is: When setting the toggle "online event = yes", all online events should be displayed, and the location should not be cleared. When setting the toggle back to "online event = no", the events should be filtered according to the location again.

cf https://framacolibri.org/t/discovery-of-online-events-without-location/23166