[download][s]Support for Column Order by header parameter

[leomrocha]

• Fixes Error 500 when making an invalid format download request.
• Adds more details to the existing download tests
• Now supports sorting the returned columns by a given order if in the /download query:

Query must be a POST and have the following fields:

{
body: MY_GRAPHQL_QUERY,
header: [col1,col2,col3]
}

and contain a valid list of column names including all the columns (fields) in the graphql query