REFAC: Adjusted out_of_bounds_value

• In most services (or all?) the out_of_bounds_value is set to 0. But this could be misleading in many cases. So change this value to a specific flag. E.g. value=-666. or similar
• It is unnecessary to set this value for each extract function, just use default values
• IMPORTANT: Maybe good to distinguish between missing values and out_of_bounds_value (-999, -888, -...)