Update EU Annex and EU Suspension Regulations Bulk Updates

This Pull Request adds:

- Possibility to delete a Regulation, with cascading to the associated objects (listing_changes or eu_suspensions);
- Marking an EU Regulation as current or not_current should also propagate to the associated objects (listing_changes);
- Marking an EU Suspension Regulation as current or not_current shouldn't change directly the is_current flag on its EU Suspensions;
- EU suspensions' is_current flag is calculated from its start and end event's effective_at date;
- EU suspensions' start and end_date are obtained from the start and end event;
- EU Suspensions' form updated to allow the selection of start and end event;
- Fixes specs and adds new specs;