Added numeric restriction to /network/{network_id}/properties.json.
Added API methods using slugs.
Added API endpoint to get ContentItems for a component based on slugs.
Added numeric restriction to /networks/{id}.json endpoint to make /networks/{slug}.json work.
Added /networks/{slug}.json endpoint.
Rearranged/refactored slugs API namespaces to eliminate duplicates.
Added tests for slugs API endpoints.