Add Contributors section to MODS and MARC metadata sections.

Closes #281 

#### 10412502
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![10412502](https://cloud.githubusercontent.com/assets/96776/3773815/7d34dc50-1918-11e4-8ce6-ecc98c8f67dd.png)

#### cf231ff4889
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![cf231ff4889](https://cloud.githubusercontent.com/assets/96776/3773814/7d349da8-1918-11e4-8004-12e26fb7cac9.png)

#### xr765qk4065
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![xr765qk4065](https://cloud.githubusercontent.com/assets/96776/3773816/7d366eee-1918-11e4-9d40-591a3dd773aa.png)