Formats endpoint

— AP + DT + (FW)
Something like this:

in spec/spec_helper.rb
```ruby
Rspec.configure do |config|
  config.before(:all) do
    VCR.use_cassette(:get_ihat_supported_formats) do
      IhatSupportedFormats.call
    end
  end
end
```

But as we discussed, we should move away from making external HTTP requests on initialization.