Add contact details to public bodies

In response to issue https://github.com/mysociety/alaveteli/issues/1266

Adds contact details to public bodies, namely:
- contact_name
- contact_title
- street_address
- postal_address
- fax
- tel
- cel

Note that this currently only affects the admin console, I haven't implemented this on the front-end views in any way.

To update the database:
```
sudo bundle exec rake db:migrate
```