Add a 'demo' graph that could be launched from the about page or somewhere on the main page.

[Richard Bruskiewich]

We wish to give the user a "pre-packaged" concept map, automatically loaded, for demonstration purposes, accessible via a link on the "About" and/or "Help" web page(s).

[Richard Bruskiewich]

<hostname>/query/demo now loads the sepiapterin reductase sample graph. initial link provided on main page (move or copy wherever needed)