Various fixes for first working version

[bob2021]

This MR contains all the fixes required for ShipStream's FedEx integration. It depends on highsidelabs/saloon-sdk-generator#10 being merged, in the meantime it points to my branch.

• Changed merging of similar schemas to only merge when all the property names and types are the same (fixes DTO objects from merged schemas having property types that are not compatible with all use cases)
• When similar schemas are merged, a property is only required if every merged schema required it (fixes DTO objects from merged schemas requiring a property in a context where it is not required)
• Fix Trade Documents Upload API (FedEx schema is incorrect, multipart/form content type throws error in saloon-sdk-generator)
• Added Account Registration API and Ship DG Hazmat API
• Updated all schemas except Global Trade, which is throwing an error on generation for some reason.
• Fixed issue where FedEx requires a trailing slash in the url path, but it is stripped by the generator.

[colinmollenhour]

Awesome!