Use original headers on csv downloads

[janette]

Replaces machine names with original CSV headers in CSV download.

QA Steps

• On a demo site, try the following request:

POST https://csvdown.ddev.site/api/1/datastore/query/cedcd327-4e5d-43f9-8eb1-c11850fa7c55/0

{
    "format": "csv",
    "properties": [
        "roadway"    
    ],
    "limit": 10
}

Note that the column header is ROADWAY.

• Now try with an expression:

POST https://csvdown.ddev.site/api/1/datastore/query/cedcd327-4e5d-43f9-8eb1-c11850fa7c55/0

{
    "format": "csv",
    "properties": [
        "roadway",
        {
            "expression": {
                "operator": "+",
                "operands": [
                    "objectid",
                    1
                ]
            },
            "alias": "objectid_plus_1"
        }
    ],
    "limit": 10
}

Note that ROADWAY is shown in caps, and alias is preserved.

If you want to try a join, try this but you will need to find the correct distribution IDs:

POST https://csvdown.ddev.site/api/1/datastore/query

{
    "format": "csv",
    "resources": [
        {
            "id": "5733123b-6b70-5ff2-8876-c4e3a7c58398",
            "alias": "t"
        },
        {
            "id": "a180fe3c-e88d-55d9-841f-912ab0c4362d",
            "alias": "s"
        }
    ],
    "joins": [
        {
            "resource": "s",
            "condition": {
                "resource": "t",
                "property": "record_number",
                "value": {
                    "resource": "s",
                    "property": "record_number"
                }
            }
        }
    ],
    "properties": [
        "roadway",
        {
            "resource": "s",
            "property": "city"
        },
        {
            "resource": "s",
            "property": "violent_crimes"
        } 
    ],
    "limit": 10
}

Known issues

• If schema property in request is set to false, the machine names will be shown. This is arguably expected behavior? The "schema" property in the request will be ignored if the format is "csv", and forced to true behind the scenes.
• In the case of a join, the properties from the second resource will have their machine names. Decided this was out of scope for this PR and will fix in the future.
• If "rowIds" is set to TRUE, adding the record_number column, we will still return machine names for all other columns as well.
• In general a lot of the CSV header logic relies on information pulled from the query or results objects which seems less than ideal.

[paul-m]

Looks like everything works... I exported and it used the CSV column names rather than the table column names. Just a few nitpicky things here about method names.