Create rake task to generate slug for objects that use Sluggable concern

Why:

* Once slug presence validation and usage is merged on to a code base, existing objects without it will become invalid and unusable

How:

* Running `bundle exec slugs:gnerate` will look for all models that include the concern, and generate a slug for each object

lib/tasks/slugs.rake

@@ -0,0 +1,8 @@
+namespace :slugs do
+  desc "Generate slug attribute for objects from classes that use Sluggable concern"
+  task generate: :environment do
+    %w(Budget Budget::Heading Budget::Group).each do |class_name|
+      class_name.constantize.all.each(&:generate_slug)
+    end
+  end
+end