This commit adds most of the optional metadata for programs. The event
related to the program's publication is an actual relationship to an
Event model. The idea is to expand on that model in the future to
include:
- A link to the event's main topic
- List of programs published in the event
- Possibly, a list of all related topics (announcement, start, results,
etc) all sharing a common 1-line header so they are linked together
- This would be used for event-related trophies
- And possibly for an event calendar
