Inform that there are no rooms when creating the schedule with a message instead of creating a room with the title "No rooms". The message also include a link to the place where rooms are created.
- 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
- Introduce plural resources for Schedule in routes.rb
- Introduce #index and #create actions for ScheduleController
- Make it possible to set a schedule as selected_schedule
