T494 Image displaye issue

Summary: The display of images pairs is not corresponding to the selected two
image diffs. The fix is to use reference to get the phid for each image.

Test Plan: Create a revision with two diffs of images.

Test the display between base and diff1/diff2.
Test the rendering of images between diff1 and diff2.
Test the inline comments also.

Reviewers: epriestley, jungejason

CC:

Differential Revision: 955