Add support for pinned messages

[Kabouik]

It would be useful to support pinning messages (for oneself or for all) and showing already pinned messages, possibly with a Go to keybind.

[d99kris]

Hi @Kabouik,

Thanks for suggesting a new feature. I think it's something that maybe can be considered, but in the short term, I will probably not have time to look into this.

In any case, I encourage anyone else interested in this feature to upvote it. This will help gauge the level of interest.

[Disonantemus]

#168 is similar to this, but only the "show already pinned" part, I did vote that, as @d99kris suggested.