perf(entities): preloads owners when drawing lists of entities/likes

When drawing lists of entities/likes with a variety of owners, many owners
end up being loaded one by one (ineffeciently). This adds a component that
walks the list and preloads all the owners into the cache in one shot.

Fixes #5949

(This PR replaces #5950.)
Use `namespace Elgg;` in this file instead of the old `Elgg_` pattern