New parameter: columnLabels - will retrieve the "real" names of the columns and put them into column_labels

Googles list-based feed changes the column name from the original
spreadsheet - no spaces, no upper case. Setting the parameter
columnLabels to "true" (default: false) will fetch the names and put
them into the column_labels property.

Signed-off-by: Martin Virtel <martin.virtel@gmail.com>