Add ability to modify configuration options

[dce]

On a recent project, I needed to prevent admins from deleting photos that are attached to other models. In a normal ActiveRecord model, this is pretty easy to do -- has_many :photo_attachments, dependent: :restrict_with_error. Since I'm using SP, though, I had to do this:

class Photo < ActiveRecord::Base
  extend SimplestPhoto::Model::Photo

  def destroy
    if photo_attachments.any?
      errors.add :base, "Photo has attachments and cannot be destroyed"
      return false
    end

    super
  end
end

It would be nice for there to be some way to modify the options SP uses, though I don't have any brilliant ideas of how to do that.