Multi lingual public nomenclature notes

Finished & cleaned up handling of public nomenclature notes (no changes to internal notes)
* added _en, _es, _fr fields to nomenclature change inputs, outputs and reassingments
* added _en, _es, _fr fields to trade_restrictions and eu_decisions (for consistency with listing changes & less awkward special cases handling)
* refactored the nomenclature change constructors to fetch note templates from I18n, rather than hardcoded values

Requires `rake db:migrate` and rails server restart (to load the translations)
Useless assignment to variable - `event`.