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
The `**kwargs` is just a bit of a safety thing, it makes it so that `__init__` doesn't throw a `TypeError` if someone (probably accidentally) defines a variable in the wiki page that doesn't exist.

For example if someone typos `category` as `catgeory`, having the `**kwargs` makes it so it will still work, but won't have a category defined. Removing it will make it fail (which completely removes the partner from the partners page).