Adds test to check for find method on Narrative, makes narrative have unique pair

Refactors to give narrative a unique id 'pair_id', allows lookup by adventure_id, objective_id, and type

[#76497278]
 On branch styling
 Changes to be committed:
	modified:   app/models/narrative.rb
	new file:   mob_order.rb
	modified:   spec/models/narrative_spec.rb