Adopt extended LayerStructure functionality

[davidorme]

Is your feature request related to a problem? Please describe.

The PR #452 adds more functionality to the LayerStructure object and will close #451. That PR has been reviewed and approved but we need to update the code in develop to use that proposed structure.

This issue is to raise a branch to make those changes. We could just merge develop directly into #452, but I want to keep the definition of the new API clear of the adoption, in case we need to update the API implementation in response to adopting it. So:

• Add more functionality into LayerStructure. #452 is being used to define what is being adopted.
• This branch and PR is being used to adopt it.