Reduce the amount of images loaded at login.

This reduces the amount of image retrival requests by removing duplicates.
It also affects the amount of image loaded messages at login (removed
about 75% of the messages for me).
This should give a small load time reduction at login depending on the
amount of items.

Some stats with my account.
Without changes:
4858 image load messages
With the GetHashCode fix:
2458 image load messages
With the images load change:
1290 image load message