Convert "preview" image transforms to new pathway

Summary: Ref T7707. Move the 220px (file uploads) and 100px (Pholio thumbgrid) previews over to the new stuff.

Test Plan: Uploaded a bunch of images to remarkup and Pholio; they generated reasonable results in the web UI.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7707

Differential Revision: https://secure.phabricator.com/D12814