browser side: contact_list update: - removed ContactPanel's "add" and "remove" method, and replaced them by a display which display all needed contact at once - first naive implementation of display: if the display change, clear and add all ContactBox. Need to be done in a more efficient way in the future - ContactBox are never deleted, and only hidden when not displayed. ContactBox are automatically created on first use (TODO: add a way to delete them for entities not in roster)