Feature: show association picture to picture on both

At the moment, when 2 pictures are associated, one is father of the other. Hence, associated picture are only shown on one of the couple.

Example : https://www.camptocamp.org/images/1605789/ and https://www.camptocamp.org/images/1621621

**Describe the solution you'd like**
In the /images pages, display also associated pictures that are father, and not only sons.