Support multiple attributes in hits for iOS / swift

[bobylito]

Bug description

Following up on #151 and after #153, swift / ios does not support the new multi-attributes hits.

How to reproduce

generate a project with the iOS target

Expected behavior

Support for multiple attributes: the UI generated should be able to display all the selected attributes.

[bobylito]

The issue is here: https://github.com/algolia/create-instantsearch-app/blob/master/src/templates/InstantSearch%20iOS/App/ViewController.swift#L29