Print the available plugins.

def print_plugins(self):
        """Print the available plugins."""
        width = console_width()
        line = Style.BRIGHT + '=' * width + '\n'
        middle = int(width / 2)
        if self.available_providers:
            print(line + ' ' * middle + 'PROVIDERS')
            for provider in sorted(self.available_providers.values(),
                                   key=lambda x: x.identifier):
                provider().print()
                print()
        if self.available_checkers:
            print(line + ' ' * middle + 'CHECKERS')
            for checker in sorted(self.available_checkers.values(),
                                  key=lambda x: x.identifier):
                checker().print()
                print()