Effective API changes:
- nil serializes to null, not empty string
- dates serialize to IETF RFC 3339 with millisecond precision, not
second precision surrounded by spaces
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
