Enable comments for image

Summary: Added line number 1 for each image and added code to display the
comments for each image.

Test Plan: Adding an image in my local directory and create a revision for it.
Click line number 1, and the comment window prompts. Adding and save the
comment. The comment shows in the differential comment list and in the inline
comment. Submit the comment. Create more comments for the image and the
"Previous" and "Next" buttons all work well.

Reviewers: epriestley, jungejason

CC:

Differential Revision: 901