Update alignment and styling of tags in show (non-edit) mode

Fixes #656 

- Center align tags list
- Update text (link) color to white to be readable on current default background color

Before:
![a_new_and_exact_map_of_asia_according_to_the_best_observations_-_default_exhibit_-_blacklight 2](https://cloud.githubusercontent.com/assets/101482/2858229/50c88bf8-d183-11e3-9e6c-79294036db1f.png)

After:
![a_new_and_exact_map_of_asia_according_to_the_best_observations_-_default_exhibit_-_blacklight](https://cloud.githubusercontent.com/assets/101482/2858230/5616cb7e-d183-11e3-9e18-e542e14dbd43.png)