refs #96 #94: remove collectstatic command and update staticfiles docs

This will resolve #96 and #94 to fallback to Django's built-in ``collectstatic`` command for collecting. The prior behavior of syncing everything all the time still works by setting ``STATICFILES_STORAGE = 'cumulus.storage.OpenStackStaticStorage'``, however for better performance it is advised to use the ``--include`` and ``--exclude flags`` of ``syncstatic`` to specify specific files and folders instead.

A new feature ticket could be opened to support ``STATICFILES_STORAGE`` by writing a new ``collectstatic`` command in django-cumulus that adds the ability to ``--include`` and ``--exclude`` files and folders by regex, however I don't believe it would be possible at this time to simply hook into Django's existing ``collectstatic`` command to achieve this.