Scale images in the upstream-training guide

Most images that exceeded the slide area were too wide.  These were
fixed by adding a 'max-width: 100%' CSS rule.  Release cycle images in
the 01-release-cycle.rst presentation were too tall because the
two-column layout was not preserved when the presentation was converted
from the ODP source document.  This change restores the two-column
layout.  The images now scale appropriately across a variety of
operating systems and browsers.  The print.css changes were tested with
the print rendering engines of Firefox and Chrome.

Change-Id: Ic5d4c3c959d37fda0d57009f282be1238388cc59
Merge "Scale images in the upstream-training guide"