Add a more descriptive message to the links-to-image section for the case that more...

Add a more descriptive message to the links-to-image section for the case that more than 100 pages link to a file.
Ths existing link to Whatlinkshere at the end of the list is easily be overseen if not scrolled to the bottom.
Fixes the (cosmetic) bug that the list shows 101 entries instead of 100.
Question: Should we make the hardcoded limit of 100 configurable via DefaultSettings?