Add Trains relationship
Update Exhibits's arbitary link spec
Update Uses's arbitary link spec
Merge branch 'model/uses' into development
Merge branch 'model/exhibits' into development
Merge branch 'development' into model/trains
Add factory for Trains relationship
Add standar spec for a relationship
Add standard model code for a relationship
Fix factory naming: should be 'factory :trains'
Merge branch 'model/trains' into development