Improve display of long metadata value lists

For metadata that can have multiple values (eg `therapeutic_area` for a `drug_safety_update` document) place each value into a separate `dd`.

### Screenshots

Before:

![screen shot 2014-09-25 at 15 08 49](https://cloud.githubusercontent.com/assets/74812/4405762/fa792696-44bd-11e4-85c7-131fd430d409.png)

After:

![screen shot 2014-09-25 at 15 08 32](https://cloud.githubusercontent.com/assets/74812/4405764/fe8c7eb8-44bd-11e4-8b8b-6b59dbc3a3ad.png)