Replace NSErrors with Error enumeration and Codable Errors

[mrlegowatch]

The initial conversion to Swift retained the implementation of making and throwing NSErrors, which are unwieldy in Swift. Additionally, the specific errors must be parsed from the localizedDescription regardless of language, which is even more unwieldy. The Codable enhancements introduce DecodingError and EncodingError as appropriate, but are limited to contexts where encoders or decoders are "in flight" (the extensions). Lastly, some APIs do not propagate errors, such as save().

• The use of DecodingError and EncodingError should be extended where appropriate
• Remaining usage of NSError should be replaced with a GarageError enumeration
• Ensure that more errors are propagated in APIs such as save(), by reducing or eliminating their catch blocks, and replacing print statements with throw.