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)
nit: split this in two lines

    # Now hosts_dict is a dictionary
    # {hostnameA: [host1, host4, host5], hostnameB: [host2, host6,], ...}