Add Goals seeds and translations

Extracted from the official United Nations Sustainable Development
Goals website [1].

[1] https://www.un.org/sustainabledevelopment/sustainable-development-goals/

db/seeds.rb

@@ -16,3 +16,6 @@ WebSection.where(name: "help_page").first_or_create!
 
 # Default custom pages
 load Rails.root.join("db", "pages.rb")
+
+# Sustainable Development Goals
+load Rails.root.join("db", "sdg.rb")