add natural key methods to EventType and UseCase
add natural key methods to EventType and UseCase

FreedomCoop/valuenetwork,django-rea/nrp,django-rea/nrp,FreedomCoop/valuenetwork,django-rea/nrp,simontegg/valuenetwork,valnet/valuenetwork,simontegg/valuenetwork,valnet/valuenetwork,FreedomCoop/valuenetwork,django-rea/nrp,thierrymarianne/valuenetwork,simontegg/valuenetwork,FreedomCoop/valuenetwork,simontegg/valuenetwork,valnet/valuenetwork,thierrymarianne/valuenetwork,thierrymarianne/valuenetwork,valnet/valuenetwork,thierrymarianne/valuenetwork