Modified title sections show

This change is related to https://github.com/alphagov/trade-tariff-frontend/pull/78 and is for the following story https://www.pivotaltracker.com/story/show/52375371. On the backend we just expose chapter numbers of the section.

Since this removes harcoded chapter ranges from section names the following commands need to be issued after deploy:

```
bundle exec rake tariff:remove:taric:sections
bundle exec rake tariff:install:taric:sections
```