Reduce the amount of weird "static" and "cache" behavior in Pholio query classes

Summary: Depends on D19922. Ref T11351. These query classes have some slightly weird behavior, including public static function loadImages(...). Convert all this stuff into more standard query patterns.

Test Plan: Grepped for callsites, browsed around in Pholio.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T11351

Differential Revision: https://secure.phabricator.com/D19923