Insert emojis and symbols with colon (:)
Description of the new feature
A lot of applications, for example Conversations, Nheko, FluffyChat and GitLab, open an emoji picker when typing :. It would be cool if Gajim would do that too.
Just opening the emoji picker will not work, because it grabs the focus and is annoying if you just want to type a :. Nheko opens a list above the text input with candidates. You can use the up- or down-arrow to select a symbol. I like this approach because it is unobtrusive and I think it makes it obvious how to select a symbol.
