Return a list of subtitle downloaders available.

def getavailable(self):
        """Return a list of subtitle downloaders available."""

        from importlib import import_module

        available = []

        for script in self.SCRIPTS:
            if have(script):
                available.append(script)

        for module in self.MODULES:
            try:
                import_module(module)
                available.append(module)
            except ImportError:
                pass

        return sorted(available)