feature: add ability to copy comment link

[indyteo]

Feature request: Ability to copy comments permalink

As mentioned in the post, it is inspired by GitHub's "Copy Link" feature on comments.

It first add a unique link for each comment, based on their ID.
For example, my reply on this post has the ID #31419, so the link would look like :

https://feedback.fider.io/posts/317/ability-to-copy-comments-permalink#comment-31419

Then, it add the corresponding HTML id attribute on a wrapping div around comments, so the page automatically scroll to the targeted comment.
On the other hand, it also create a highlighted state in the ShowComment component that slightly mutate the comment background (a bit darker than others) to stand out. When a click is performed outside of the comment's area, it get back to normal and the hash is removed from the URL (the part after the #).

Finally, an action in the comment's drop down, target the current comment (set the URL in the navigation bar, triggering the comment highlight and scroll), and copy that link into the user's clipboard. A feedback indicate whether the copy was successful or not (due to the lack of support of the Clipboard API by some old outdated browsers), and invite people to manually copy their page's URL if not.

If the hash don't match anything is simply get ignored, and if it looks like a comment reference but we're unable to find it, a notice is shown to the user, because it may happen when the original comment got deleted, or the URL was manually modified and is now invalid. It get instantly cleaned up to avoid further share of a partially invalid link.

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I never really played with URL's hash before and found it funny to do this, this is why I decided to train with this idea, even if it only has 2 votes (which means none, except from the submitter and me 😆), and it only took me about an hour so it was fun 😄

[almereyda]

@indyteo Would you like to rebase this branch on main, or merge it again?

Then we could try to find someone for a review. Eventually you can also request a review?

[indyteo]

Hi @almereyda, I can have a look if it's not much work 👍