Use Orm Adapter gem to handle conditions/order from associations

This would be an approach using Orm Adapter to handle the relation query in Simple Form.

But, after finishing that, it came to my mind that actually passing options as a hash in associations is deprecated in Active Record, isn't it?

If it is, I'd rather stop supporting this way and just load the relation, which should apply its own conditions instead of doing that ourselves. We can figure what needs to be done with mongoid later if needed.

Thoughts?

Related to #759.