Tags for non default resource class

[Kookabura]

It's good to have an ability to use tags for custom classes. I've added parameter $class for that.

[theboxer]

Could you explain how this works?

[Kookabura]

As we can store different resources in site_content table and they differs only by class_key attribute it's good to have an ability to select them from database with Tagger filtered by class key. For example I use it for selecting ecommerce products from site_content by tags. I can't get anything with custom class_key without this fix.