Basic branding for Hydra North / UA Libraries

Copied two files from the Worthwhile gem into the main Hydranorth app and modified them; added the hydranorth.png to assets; modified the blacklight locale.

Note that it is necessary to restart unicorn to get the new sufia.en.rb locale to take effect (which is what changes "Repository" to "Hydra North" on the front page).

```
sudo pkill -f unicorn_rails
sudo unicorn_rails -D -c /var/www/sites/hydranorth/config/unicorn.rb
```