Allow International Development Funds to be viewed

([Trello ticket](https://trello.com/c/QUI3M1Kx/226-dfid-finder-add-support-to-specialist-frontend-for-rendering-international-development-funds-2]))

 * Add InternationalDevelopmentFund presenter
 * Add cucumber spec mirroring CMA cases.
 * Fix CMA case cucumber spec (was looking for nil)

Development/Test only:
 * Add launchy gem to allow save_and_open_page in test suite in future.

- [ ] Update Gemfile to use new version of gds-api-adapters when https://github.com/alphagov/gds-api-adapters/pull/181 is merged.
I know this indentation style for `delegate` is pretty common in our apps, but it's pretty nasty. Can we make a clean break and use something like:

```ruby
delegate(
  :application_state,
  …
  to: :"document.details",
)
```