Issue title: Pivot: Should the tab style be removed?
 Issue body: ![image](https://cloud.githubusercontent.com/assets/1382445/15629721/5b2e6408-24d5-11e6-9874-58dbf12b72af.png)

I don't see design specs for this variant (both small and large tabs). Are these no longer part of the design language?
 Comments: 
 Comment 0: This issue was moved to OfficeDev/office-ui-fabric-js#57
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