Keep crosshair parameter as long as map is not moved/zoomed

The crosshair parameter is removed from the URL after the page is loaded. This led to confusion as with page refresh (F5). the crosshair disappeard. See https://github.com/geoadmin/mf-geoadmin3/issues/1200 /  https://github.com/geoadmin/mf-chsdi3/issues/469 and others.

This PR keeps the crosshair parameter in the url as long as the map is not panned or zoomed.