Write and use refresh helper method to test AJAX-functionality

[eliotsykes]

Used this refresh method on a project to ensure the page was always refreshed (IIRC, when the URL had a fragment identifier, e.g. http://localhost:3000/#/products, the refresh wouldn't work when it was a visit current_url, the refreshEnforcer random param was needed):

  def refresh
    url = URI.parse(current_url)
    if url.query.blank?
      url.query = ""
    else
      url.query << "&"
    end
    url.query << "refreshEnforcer=#{rand}"
    visit url.to_s
  end

Introduce this to rspec-rails-examples to test that an AJAX-dependent change has persisted.