The index.rst page for Cinder was not well suited
to the new openstackdocstheme that was created. This
resulted in the page just looking like a disorganized
set of links with no visually defined topics or
explanation.
With this patch I emulate the look of the Keystone page
by properly indicating the different topics in the page
and add some text to describe each of the sections. I also
update some of the old 'Block Storage' pages to use a 'Cinder'
heading for consistency.
Change-Id: I341e8340b960946a86f4ff8fbee3624531b375af
b156d24b6e