Add navigation for the business plan documents.

[kixxauth]

The overview page has no links to the business plan documents. We should probably consider adding this, since I think it's an important part of the "owners manual" to the company.

[kixxauth]

The current location of the biz model documentation is here:
http://www.fireworksproject.com/pages/biz/search-and-pivot.html

However, there is also an outstanding issue for this URL on the main website repository as well:

https://github.com/FireworksProject/www.fireworksproject.com/issues#issue/4