[Bug 968888] Model changes to enable post event data.

* Rename expected outcome field.
* Add model field for the real outcome.
* Add field for the actual attendance.
* Add flag to seperate events with old metrics.
[Fix bug 968888] Add post event data form.

* Make past events with old metrics compatible with new metrics
* Force new metrics in current & future events
[Fix bug 1004777] Display post-event metrics on event page.