Indicator if issue/PR bookmark has been updated

[BasThomas]

Depends on #682

From #601 (comment)

Think this is quite a tricky one, depending on the type of bookmark. What is "updated"?

[Sherlouk]

In my head this was exclusive to Issues/PRs, if the thread has been updated since you last looked

[BasThomas]

Yep, that can work. At least as a first step, although I think Issue+PRs will cover pretty much everything huh

[Sherlouk]

Marking as low though because for the most part (granted there are exceptions) you'll be subscribed to the post anyway. So you'll receive a notification through typical means, was more of a "In case you missed it" warning I dunno