Add support for emojis and stickers

One simple way to collect some information about emotions of users (#165) is to allow them to add emojis and stickers in an easy way. Maybe we could add some autocompletion for emojis, and some library to add stickers (and gifs), maybe even from some remote sticker and gif services.

oh god... >.<

What, you are missing meme generator? I think we should add that as well.