Fix contextpopup

contextpopup was broken on desktop because of https://github.com/geoadmin/mf-geoadmin3/commit/b0831a4e71d057d911b63f77b610f9817f34d803

I revert this fix and apply the old behavior : 
 - mobile version -> long touch
 - desktop version -> contextmenu event if exist otherwise long touch

I made this because IE 11 on mobile has an event contextmenu but not triggered on long touch like on Surface

Tested on desktop (chrome,ff,ie10) and mobile (IE11 Surface, IE 11 phone,  safari)