Remove click events from Filter category labels (#102)

This pull request addresses issue #102, removing click events from Category labels in the Filter. It turns them instead into just regular text. Some additional white space cleanup is included.

Padding was required for the categories since they lost their former span padding. Tested on both Firefox and Chrome and the layout is identical.

Adding @andreieftimie and @whimboo for visibility.
+1 for Henrik's suggestion. Let's just keep it simple.
We'll also remove the need for the `:first-child` pseudoselector.