Move flow chart from old-html to Sphinx

Move flow chart from old-html to Sphinx

Get rid of the remaining HTML page generated from old-html/, and all the
machinery that was there just to generate and link to these pages.
The images used by the flowchart still remain in old-html/ and there is
a target to copy them to the output, but this is significantly simpler
than what it was.

For now, replace the flow chart with raw HTML within rst; using
something like sphinx.ext.graphviz could probably work better.
<td align=...> did not work when embedded into a Sphinx-generate page;
replaced with <td style="text-align:...">.

Change-Id: Icbcccd36a9cc157a5a8efe1e9054d6a6741c83ca