WebApps -Sort By - multiple fields

Allow setting multiple fields to sort a WebApp by
When you sort WebApp items in a List by for example weighting, but not all Items have a weighting, it falls-back to sorting by last-updated.
Khy has requested that we adjust the Liquid parameters so that it's possible to sort by more than one field- the first field being the main sorting field and any following ones serving as fallback-options if any Items remain unsorted.