Link macro thumbs and show an exact page count

Summary:
Some of the improvements from T175: link macro thumbnails to the full image, and
pull an exact count out of the database.

Test Plan:
Clicked a thumb, looked at pager.

Reviewed By: tuomaspelkonen
Reviewers: tuomaspelkonen, tomo
CC: aran, tuomaspelkonen
Differential Revision: 397