Duplicated debug message

Before calling the parser, the JSON received is printed if log level is DEBUG:
``` python
logger.debug('Data received: %s', post_data)
message = compose(self.template_path, parse(post_data))
```
and is printed too the very moment we call the parser:
``` python
def parse(json_str):
    logger.debug('received: %s', json_str)
[...]
```

So second time is not necessary.