R1:431c57688e0d

Improve performance of project list view

Summary:
D477 added functionality to the project list view but had a couple of
performance issues that I missed in review, because it took the query count for
the page from around 3 to as many as 300, including up to 100 heavyweight search
index queries.

This fixes the two simple N+1 query problems. This general pattern of data
access often occurs:

COUNTEREXAMPLE
$cats = load_cats();
foreach ($cats as $cat) {
$cats_hats = load_hats_for_cat($cat);
//…