(bug 56807) Localize logo for Welsh Wikisource

This patch changes the logo for Welsh Wikisource
from the default English logo into a localized
version requested by the community; see bug for
URL with more details.

The file has been protected on Commons against
re-uploads and moves for all users except admins.

Bug: 56807
Change-Id: I48ec7465078e79a5aac705ef4c7c8cc204fb1b8c