It was needed to use the id instead of the guid in the html attributes of the events in the admin schedule
- move SchedulesController#update action - split it into an #create/#update and #destroy action and use these actions in the JS code
- Only use JS for the drag&drop functionality and to the set/alter the time and rooms of the EventSchedule object. - Introduce has_many :events, through: :event_schedules association to get unscheduled event easily