Gold partners: add categories, support filtering

Adds categories to the gold partners, and a filtering bar at the top of the partners page:

![partner-categories](https://cloud.githubusercontent.com/assets/9033/3557045/2609ffca-092b-11e4-80df-c27aad59db65.png)

:eyeglasses: @bsimpson63 @umbrae @powerlanguage
There's no real "effect" as in an animation or anything, it just happens instantly. The end result is that all the partners from a category different than the one that was clicked are hidden.