Add older/newer links in front of diary, comment, issue, block pages

[AntonKhorev]

For consistency, this adds previous/next page links on the top of every page where it's also at the bottom. See #4646 (comment) for reasoning.

[nenad-vujicic]

This works great on my side, thank you very much!

Wild idea: since we already have decision procedure, which answers the question "do we have multiple pages?", why don't we use it for hiding pagination buttons when they are not required / usable?

[nertc]

Tested and works perfectly. Every occurrence of "shared/pagination" has its own pair on top of the page.