Add EventMetric and EventMetricOutcome models.
Show EventMetric to base content.

* Fix /stats/ URL conflict with admin URL.
* Register new models to admin.
* Minor fixes in new models Meta.
Replace old metrics with new metrics.

* Remove unused code from old metrics.
* Change templates to handle new metrics.
* Minor compatibility fixes between old and new metrics.
* Add factory for new metrics
PR changes.

* Fix error message on IntegerField
* Fix tooltip
Change TextInput widget to spinbox.