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

app/serializers/event_schedule_serializer.rb

@@ -0,0 +1,14 @@
+class EventScheduleSerializer < ActiveModel::Serializer
+  include ActionView::Helpers::TextHelper
+
+  attributes :date, :room
+
+  def date
+    t = object.start_time
+    t.blank? ? '' : %( #{I18n.l t, format: :short}#{t.formatted_offset(false)} )
+  end
+
+  def room
+    object.room.try(:guid)
+  end
+end