FLUID-5516: Updated build site to match new design.

@jobara @acheetham - I've updated the build site to match the new designs. Can you check to make sure I got all the right demos and that the links all go to the right places?
Regarding the little "external link arrow" icons: When did these get into the designs? They appear on almost every single link, which makes them seem a bit redundant, and clutters the page unecessarily (I wonder this about the fluidproject.org site, too). Do we really need them?