API: JSON Exports now camelCased

In "forward-looking" conformity with the Beacon v2 API, the JSON attributes of the API responses has been changed from snake_cased to camelCased. Please adjust your code, where necessary.

Some examples:

• call_count → callCount
• error_message → errorMessage
• child_terms → childTerms
• variant_type → variantType
• results_handovers → resultsHandovers