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.
We want to apply the padding to the To: field, but not the `float: left` or `width: 6.1em` offsets that are also a part of the `first-child` selector. I we had one general `label` target we'd end up applying that css everywhere and end up floating the To: field in the wrong location:

![tofieldsignlelabeltarget](https://cloud.githubusercontent.com/assets/3660661/3201229/6d8f4c90-ed85-11e3-9112-cfc3a53fb9a4.jpg)

We could however leave the html label markup for the To: field untargeted by css, and let it squish together if you prefer. That would result in a difference in the layout from what had been Andei's previous return to align the labels. Before and After provided below:

![tofieldbefore](https://cloud.githubusercontent.com/assets/3660661/3201282/0ac9c634-ed86-11e3-83cb-97ec5ab0fad8.jpg)
![tofieldnocss](https://cloud.githubusercontent.com/assets/3660661/3201284/0fa73786-ed86-11e3-82db-312ec9711c7e.jpg)

But it does technically change the spacing from what we had. That was the reason why I used `nth-child` to target the To: field by itself and apply its correct padding. Maybe there is another way to do it, let me know if that is the case and I will try.