Add batch photo import by timestamp and batch import preview.

Add batch photo import by timestamp and batch import preview.

A massive improvement to the "click-and-pray" netid-only importer.
This changeset provides a preview of the photos that will be imported,
allowing for review before committing all the changes, as well as
progress bars (since loading large photos is a time-consuming task).
In addition, we now support importing large sets of photos based on
relative timestamps.  This will work provided you have exactly the same
number of photos to import as you do people in the database without a
photo.