Store references in page_props and cache
This stores references in page_props during links update in
compressed JSON form. If the size is too big, it's broken up
in several parts to fit, which is very unlikely to occur more
When the data is retrieved from the db, it's always cached. If
set in config, it's also saved in the cache on parse. If not,
the cache is invalidated when references are modified.
There's a soft dependency on the core change