Description of project affiliations

Modifies the projects page to better describe the relationship between NF and its projects.  It defines "NumFOCUS Projects" to be projects with a comprehensive association, "Supported Projects" to be grater-grantee associations, and "Affiliated Projects" to be projects we think are groovy, but don't have an official relationship.

@fperez, you were going to work on this.  Here is a first stab to get you started.

closes #30