ApiPageSet lazy loads content models
A preceding patch, I7eff0bff, adjusts multiple Title methods to load the
content model from the database if it is not known. This patch
adjusts ApiPageSet to query for the content model with the initial data
load rather than allowing the lazy loading to pull in the content
model one at a time as requested.
(cherry picked from commit 2ddd236cdf786f02283ef3ce4cc11777598fd55e)