Add link to deleted posts for people who can see them

[cellio]

meta:292503

Curators can see deleted posts, but they don't have a navigation path to deleted top-level posts. In general, we want people with privileges to be able to "audit" the use of those privileges. The approach I proposed in an answer there is to build on the sidebar widget that currently contains "moderator tools" and "admin tools". These are already context-sensitive (you only see them if you're a mod/admin), so we could add a link to the "recent deletions" page here, and later a filtered flags view (curators can see certain flags but not all of them).