Fix using InputArgument class constant for addOption

InputArgument class constants were used instead of InputOptions class constants for Command::addOption mode parameter (The numerical values were correct, though)
InputOption::VALUE_REQUIRED means that value is required for the option (e.g. --iterations=5), the option itself is still optional.

InputArgument::OPTIONAL === InputOption::VALUE_REQUIRED, however InputArgument::OPTIONAL should be used for Arguments, not for Options.