Tags Redux: styling tags

This PR styles the tags closer to what they were before we removed Jquery UI. Personally, I preferred them with some styling to show they were distinct from the annotation body. 
![tags](https://cloud.githubusercontent.com/assets/521978/4004591/9ce489f8-2983-11e4-9c1c-fe5d6ebc0c11.png)

Meant to resolve: https://github.com/hypothesis/h/issues/1426
When styling clickable elements it's preferred to put the padding on the anchor element. That way you ensure the entire element is clickable. Right now we have a button like object but the hit area and hover styles only apply when you mouse over the text. This issue is compounded by the fact that the entire card has a pointer cursor.

![screen](https://cloud.githubusercontent.com/assets/47144/4008334/b57b84ce-29d5-11e4-9338-4cbe8edea8f3.png)