Implement support for exporting entities into JSON files and add UI for import
- This adds support for exporting (some) entities and can be extended to support more entities.
- It also adds support for importing using the UI.
- This is currently the import/export UI: - it could be improved in future eg. moving the export links to other config pages in CiviCRM?
There is a breaking change in the JSON file format - instead of relying on the filename the entity type is now specified in the JSON. I think this is best as it avoids any errors and also allows in the future for a single file to contain multiple entities etc.