rules: add two management commands

This patch adds two management commands: 'addsource' and
'defaultruleset'. The idea is to be able to create from
command line objects in the database to have a ready to
use scirius (for example in the case of SELKS).

'addsource' can be used to add and update a source. Its syntax is as
follow:
 python manage.py addsource "ETOpen Ruleset" https://rules.emergingthreats.net/open/suricata-2.0.1/emerging.rules.tar.gz http sigs

'defaultruleset' will create a ruleset using all defined sources and
taking all categories available in the sources. The syntax is as
follow:

 python manage.py defaultruleset "ETOpen based ruleset"
suricata: add management command 'addsuricata'

This patch adds a management command 'addsuricata' that creates
the suricata. The syntax is as follows:
 python manage.py addsuricata Suri "Suric attack" /tmp/ "ETOpen based ruleset"