Add ability to specify extraTables explicitly for MySQLVehicle extract

[opengeek]

Example:

        {
            "vehicle_package": "",
            "vehicle_class": "\\Teleport\\Transport\\MySQLVehicle",
            "object": {
                "extraTables": [
                    "my_fancy_table_name_here",
                    "another_fancy_table_name_here"
                ],
                "excludeExtraTables": [

                ],
                "excludeExtraTablePrefix": [

                ]
            },
            "attributes": {
                "vehicle_package": "",
                "vehicle_class": "\\Teleport\\Transport\\MySQLVehicle"
            }
        }

Tables specified explicitly in extraTables will use the MODX table_prefix unless the tables are also listed in excludeExtraTablePrefix.