Move activerecord model to app/models
Make class methods really private

If a class method should really be private, this example doesn't work:

  class Foo
    private
    def self.foo
      "This is not a private method"
    end
  end

  Foo.foo # => "This is not a private method"

Instead, we should do the below to make class methods private:

  class Foo
    class << self
      private
      def foo
        "This is a priate method"
      end
    end
  end

  Foo.foo # => NoMethodError: private method `foo' called for Foo:Class