New associations and models: schedule versioning

For the schedule versioning in the admin interface (having multiple possible shcedules) we need to change some models and associations. It has also been create a rake:move_events_attributes task to migrate the data.

User Interface addapted to make use of the introduced associations and models

lib/tasks/several_schedules.rake

@@ -0,0 +1,24 @@
+namespace :data do
+  desc 'Move the start_time and room attributes from Event to EventSchedule'
+
+  task move_events_attributes: :environment do
+    Program.all.each do |program|
+      schedule = Schedule.create(program: program)
+      program.selected_schedule = schedule.id
+      program.save
+      program.events.each do |event|
+        unless event.start_time.nil? && event.room_id.nil?
+          # we can not use .room as this relation has been removed
+          EventSchedule.create(event: event,
+                               schedule: schedule,
+                               start_time: event.start_time,
+                               room_id: event.room_id)
+          event.start_time = nil
+          event.room_id = nil
+          event.save
+        end
+      end
+    end
+    puts 'The start_time and room attributes has been moved from Event to EventSchedule'
+  end
+end