Branch sf3

fix symfony3 php depreciations ;
add time to event dates ;
add new moderator field on events ;
misc improvements form styles ;
adapt webpack config for styles sheets ;
add a new page 'events participation' in menu person, that list all events participation for a person ;
subscribe a person to an event from person context ;
improve message translation ;
add a first step to pick center in new event form ;
add events in history timeline ;
export participations list for an event ;
add event administration pages ;
add remove participation and remove event feature ;
fix the way the bundle compile assets ; This modification will require to update Chill-Standard to the latest version. At least, the file webpack.config.js should be upgrade to the last version
fix redirection when only one participation edit ;