Event model improvements

- Drop selected_event_schedule function
- Rename scheduled_room and scheduled_start_time to room and time as if there is no selected_schedule, the event is not scheduled.

app/controllers/proposal_controller.rb

@@ -15,7 +15,7 @@ class ProposalController < ApplicationController
   def show
     # FIXME: We should show more than the first speaker
     @speaker = @event.speakers.first || @event.submitter
-    @event_schedule = @event.selected_event_schedule
+    @event_schedule = @event.event_schedules.find_by(schedule_id: @program.selected_schedule_id)
   end
 
   def new