move explain link to prev/next button row

Extension of https://github.com/duckduckgo/zeroclickinfo-spice/pull/1241

Moved the "Explain" link away from the "More at" and placed it beside the "Prev" button

//cc @mattr555 @jagtalon @chrismorast 

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![image](https://cloud.githubusercontent.com/assets/873785/5413412/3fd203b2-81e4-11e4-8830-cc3b33c5d71e.png)


![image](https://cloud.githubusercontent.com/assets/873785/5413418/55df0b28-81e4-11e4-9a2c-a8155f40f23f.png)


![image](https://cloud.githubusercontent.com/assets/873785/5413441/a6030abe-81e4-11e4-9fe8-2d7ab78d4e23.png)