ENHANCEMENT: Export resources nested structure as flat columns

[camfindlay]

For each resource (and we don't know how many a dataset will have) we should be able to parse out each from a nested json into a column per property structure.

Eg. resource.1.name, resource.1.url, resource.2.name, resource.2.url etc

Could be a flag --flat_resources passed in the cli to include this in the export.