Updated: About OpenStack Object Storage Document

One of the TODO entries was to provide a more comprehensive overview
of Object Storage/Swift than was already written. This is a first
attempt at making it better.

This patch also uncomments a line within the 'admin-guide-cloud' book
that doesn't reference the common 'about-object-storage' page like others
do. I've reverted this and tested thoroughly, not sure why this was there.

In addition, I updated a few other pages where they lacked certain
clarity. For example- the 'Getting Started' page provided only a very
basic overview of the components and without going into too much detail
I added further information. There were also a few English syntax changes
throughout some of the other pages.

Change-Id: I1952d9e1882fc962320304759110a2ccbc50de82
backport: havana
(cherry picked from commit c5aaf5424cec06f83c2dcf4730f3042ec4ea73a4)