Deleting a doc deletes annotations made from it, even if those annotations are linked to other docs

[MartinFoys]

Deleting a doc deletes annotations made from it, even if those annotations are linked to other docs. So, basically, deleting a parent doc automatically deletes annotations related to it, regardless of whether they are linked elsewhere.

[MartinFoys]

Note: this was discussed in detail by @akstuhl and @NickLaiacona in July of last year, with this precise issue identified as a problem to be addressed, and summarized in #97