adding SQL database support for actor

[randomor]

So, I commented out:

 # raise Errors::NotMongoid, "Must be included in a Mongoid::Document" unless self.ancestors.include? Mongoid::Document

in actor.rb. And it looks like it's still working with my User<ActiveRecord::Base model. I only needed to make a new Mongoid based Activity model. As a noob, am I wondering into dangerous territory? It would be really cool if this also support my current data schema.Thanks for the great work!

[christospappas]

This will probably cause issues when loading associated models but I haven't tried it. If this works for you, it would be great if you could submit a pull request with your changes and a test that shows it works with active record.