[Fix bug 968888][Fix bug 1011180] 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.
PR update.

* Fix error messages in outcome/attendance.
* Make estimated attendance readnly in post event data form.
* Don't show new metric button in post event data form.
* Untabified.
* Make is_past_event a property
[Fix bug 1004755] Add passive report for post event data.