Deprecate string options in URL helpers

Fixes https://github.com/rails/rails/issues/16958

I pretty much implemented @bronzle's fix in the issue comments, so he should have credit too.
we could do, something more like:

```ruby
if options && deprecated_options = options.keys.any? { |k| DEPRECATED_STRING_OPTIONS.include?(k) }
  ActiveSupport::Deprecation.warn("Calling URL Helpers with string keys (#{deprecated_options.join(', ')}) is deprecated. Please call with symbols instead.")
```

or something even better