better JSON responses for uploads

[tomkralidis]

(moved from wmo-cop/wmo-oscar#33)

Doing a WMDR upload to the M2M API via pyoscar results in the following:

pyoscar upload --xml ../msc-wigos-metadata/out/2202102.xml --api-token API_TOKEN --env dev
Running against OSCAR dev (https://oscardepl.wmo.int/surface/rest/api/)
{
    "logs": "The XML has been parsed with the following exceptions/issues:\nREF_8: The value for coordinates \"latitude = -121.2\" is invalid. Information for the \"facility/geospatialLocation/location\" is discarded.\nREF_8: The value for coordinates \"longitude = 61.766666666666666\" is invalid. Information for the \"facility/geospatialLocation/location\" is discarded.\nREF_5: ReferenceType for \"facility/geospatialLocation/geopositioningMethod\" with URL \"http://codes.wmo.int/wmdr/GeopositioningMethod/\" could not be found. Information for \"facility/geospatialLocation\" is discarded.\nREF_8: The value for coordinates \"latitude = -121.2367\" is invalid. Information for the \"facility/geospatialLocation/location\" is discarded.\nREF_5: ReferenceType for \"facility/geospatialLocation/geopositioningMethod\" with URL \"http://codes.wmo.int/wmdr/GeopositioningMethod/\" could not be found. Information for \"facility/geospatialLocation\" is discarded.\nREF_8: The value for coordinates \"latitude = -121.236667\" is invalid. Information for the \"facility/geospatialLocation/location\" is discarded.\nREF_5: ReferenceType for \"facility/geospatialLocation/geopositioningMethod\" with URL \"http://codes.wmo.int/wmdr/GeopositioningMethod/\" could not be found. Information for \"facility/geospatialLocation\" is discarded.\nREF_8: The value for coordinates \"latitude = -121.2367\" is invalid. Information for the \"facility/geospatialLocation/location\" is discarded.\nREF_5: ReferenceType for \"facility/geospatialLocation/geopositioningMethod\" with URL \"http://codes.wmo.int/wmdr/GeopositioningMethod/\" could not be found. Information for \"facility/geospatialLocation\" is discarded.\nREF_6: No value found for the element \"facility/territory/validPeriod/../beginPosition\". Information for this item is discarded.\nREF_4: A facility with alias \"FORT SIMPSON CLIMATE\" already exists. This alias is discarded.\nREF_6: No value found for the element \"faciliy/responsibleParty/validPeriod\". Information for this item is discarded.\nREF_3: The element \"ObservingFacility/\u2026/programAffiliation\" with WMO306_CD = \"GCOS\" is not linked with any observation under \"observation/programAffilation\", thus it is discarded.\nREF_3: The element \"ObservingFacility/\u2026/programAffiliation\" with WMO306_CD = \"WIGOSnonAffiliated\" is not linked with any observation under \"observation/programAffilation\", thus it is discarded.\n",
    "xmlStatus": "SUCCESS_WITH_WARNINGS",
    "id": 11
}

1. can the logs property be changed to a list of messages
2. if not, can the newlines in the logs property be encoded as \\n instead of \n for better pretty printing/readability at least?

Item 1 would be preferred if possible.