Tidy up models_require.rb

[paulrayner]

The file spec/support/models_require.rb is used by some of the specs to require the domain objects. There must be a better way to do this. Plus, when new files are added it's just another file to update that could slip through the cracks.

I just added routing_service to this file, which makes it even more poorly named. Rails calls these objects 'models' but they are not. There is only one domain model in this application for cargo tracking, and it includes all the objects in this file. Each object is not its own model.