Update the ActiveRecord backend to not save entries for records that aren't saved yet.

 - If a state machine has :action => nil on it, the saving of the record and the changing of its state are decoupled. This means that the state can be changed and state machine callbacks can be called on a new record without an ID yet. That means its unsafe to try to create associated records until the record is saved. The state machine callbacks also get called when the record is saved even with action => nil, so I think this means we can just not create records if the record is new.