Use photo id when available.

Photo id is a long that uniquely identifies a photo associated with a
contact. It only handles low-res photos, but that's what's used in the
call log anyway.

This commit uses photo ids instead of thumbnail URIs if the photo id is
available, since that's more efficient for storage purposes. In fact, if
a photo id is available it does not even bother storing the URI.

This will make a significant difference in terms of storage when I will
use the call log table to store cached contact information, including
the photo id and thumbnail URI.

Bug: 5101753
Change-Id: Ia60e3ce33763fe3744208763befbaf4489d60bdd