Style case-study page

Add some styling for a case study show page.

- Setup IE specific stylesheets
- Improve the slimmer setup
- Add presenter to interpret content store data
- Use components to build show page
- Add minimal styling for things not covered by the show page
`10` is due to some languages having many words for pluralisation [for example in arabic](https://github.com/alphagov/whitehall/blob/master/config/locales/ar.yml#L38-L44). It is the way this is done in whitehall to get a generic pluralised string.

This is a presenter not a controller it's job is to get the data ready for display. I am not wedded to the i18n call being here, it could easily be in the template. When we start creating more templates for different formats it would be nice to have it abstracted away and the presenter seems like the right place for it to me.