Server-created heading products show genre icons.

Still need to do the tips ("you can add your wp.com!") and anchor links.
Anchor links work for server-built category heading products.

Got rid of the url_slug param being passed all over. Instead, in views.py
 we put a profile_slug property on Flask's global g object that can be
accessed in the templates.

Still need to make the tips show up for blog and twitter headings.