Add different themes.

[shaunagm]

This builds on #4. It would be cool to add a variable into the path to the graphics images. Instead of "data/img/ankhIcon.png" use something like "data/themes/default/ankhIcon.png" and "data/themes/modern/ankhIcon.png" and "data/themes/neon/ankhIcon.png". For a quick fix, the theme could be hardcoded, or set as an environment variable. As a longer-term project (something a student might do outside of this event) would create an Options menu to set the theme.`