add time_zone to events

.../admin/communication/websites/agenda/events_controller.rb

app/helpers/admin/application_helper.rb

app/models/communication/website/agenda/event.rb

app/models/communication/website/agenda/event/with_cal.rb

app/models/communication/website/agenda/event/with_time.rb

...dmin/communication/websites/agenda/events/_dates.html.erb

...admin/communication/websites/agenda/events/_form.html.erb

config/locales/communication/en.yml

config/locales/communication/fr.yml

...1_add_time_zone_to_communication_website_agenda_events.rb

db/schema.rb

test/fixtures/communication/website/agenda/events.yml

test/models/communication/website/agenda/event_test.rb