[#19] Polish footer
[#43] Add Copernicus to Topic categories

To add a value that is not part of the original topic categories
vocabulary:

1. Add the tag to the `tags_to_include` list on plugin.py

2. Add an entry to the CATEGORIES dict with the name and title

3. Reimport the harvested documents:

    paster harvester import -p dataset_name

  or the following for just one dataset:

    paster harvester import -p dataset_name

4. Reindex