return values from api_proxy should lead to appropriate HTTP error codes

[ElDeveloper]

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The qiita_pet/handlers/api_proxy module returns data in the form of {'status': '[error | success]', 'message': '...', 'data': ''}. Regardless of the value of the status key, the return code appears to be 200 for most requests. For example see qiita_pet/handlers/api_proxy/base.py.