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/models/event_schedule.rb

@@ -0,0 +1,5 @@
+class EventSchedule < ActiveRecord::Base
+  belongs_to :schedule
+  belongs_to :event
+  belongs_to :room
+end