Run ActiveRecord generators by default

After enabling Zeitwerk mode I unintentionally disabled ORM default
generators (9f1b6b0).

This commit brings them back.

[fixes #351]

lib/merit/generators/install_generator.rb

@@ -12,6 +12,10 @@ def copy_migrations_and_model
         template 'merit_point_rules.erb', 'app/models/merit/point_rules.rb'
         template 'merit_rank_rules.erb', 'app/models/merit/rank_rules.rb'
       end
+
+      def run_active_record_generators
+        invoke 'merit:active_record:install'
+      end
     end
   end
 end

lib/merit/generators/merit_generator.rb

@@ -11,6 +11,10 @@ def inject_merit_content
         end
       end
 
+      def run_active_record_generators
+        invoke 'merit:active_record:merit'
+      end
+
       private
 
       def model_exists?

lib/merit/generators/remove_generator.rb

@@ -5,6 +5,10 @@ module Generators
     class RemoveGenerator < ::Rails::Generators::NamedBase
       source_root File.expand_path('../templates', __FILE__)
 
+      def run_active_record_generators
+        invoke 'merit:active_record:remove'
+      end
+
       private
 
       def model_exists?