Pill text

The pill label text style is pretty classy, and @mperrotti has a design that uses it outside the pill shape for member title (not role). This PR pulls out the text styles into a separate placeholder class and creates a new `.pill-label--text` variant that will only apply the text styles.

I'd like to transition toward requiring a base `pill-label` class in addition to the variant class for all uses of pill labels so that we don't have to double up our selectors in CSS when extending the text %placeholder and the shape %placeholder.

![screen shot 2014-04-11 at 12 57 00 pm](https://cloud.githubusercontent.com/assets/1885153/2682420/b6959cb2-c19a-11e3-8166-d24e32b86a05.png)

PHOTOGRAPHER text here:
![member title](https://cloud.githubusercontent.com/assets/1885153/2682410/9987f840-c19a-11e3-84be-23cac3fa3fdd.png)