Summarize data

Please, check my code!
I forgot to include some kind of readme.st. To test custom command:
python manage.py summarize [date YYYY-MM-DD] [--nodeletion]
If you pass no parameters it summarizes current date minus 15 days (single day and no a 15-days period)
I think this is more readable:

```python
speed = determine_speed(project, status_4xx, status_5xx,
                        status_none, avg_time, total_response)
project_list.append(speed)
```