Custimoze report to display categories as tabs

Add a new show_tabs template to keep the ep readable. It is used when
the report (new columns section_tabs in reports) is customized to group
graphs in the same category in a tab. Rewrite the ploting js code to
allow choosing which graph to display.

Remove the top button of each graph and put it in the TOC header, so
that is always visible. Scroll the page by hand when links are clicked
in the TOC.