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)
@haplo: 
> nit: it's good practice to add a trailing comma in the last element of dicts, it makes 
> reorganizing items or adding a new one easier.

A nice perk of doing that is that ```git blame``` will show who wrote the line, instead of who added the comma at the end.