Use SVG graphics in HTML docs

 * Pre-convert SVG images to PDF with Inkscape

 * Do not pre-convert SVG to JPG, let Sphinx choose the best image
   format (SVG or PDF)

 * Optimize diagram scaling for consistent font sizing and clean PDF
   layouts

Change-Id: I22285f5284f3c396ebe98392fca3dc731b01d6fa
Reorganize storage reference architecture

 * Expand Storage Nodes subsection of Logical Setup with HA
   considerations for Ceph and Cinder LVM

 * Fix nesting level of the Neutron vs. nova-network section so that it
   and Savanna Deployment are subsections of Technical Considerations

 * Replace Swift specific Object Storage Deployment section with new
   Storage Architecture that covers all aspects of storage for OpenStack

 * Ceph deployment diagram for Storage Nodes subsection

 * Expanded explanation on when to use dedicated Swift nodes vs
   deploying all Swift services on controllers

 * Describe Ceph RBD support differences between vanilla Havana and
   Mirantis OpenStack 4.0

Change-Id: I9048a8299294716fe526f18eeab530c39477c4f2