Introduce visual user preferences

[flbulgarelli]

It would be nice to allow users to enable some visual customizations.

Based on many experiences, some of these may be:

• dark-mode
• emoji-less mode: some people don't like emojis at all. Removing them on a user basis is trivial, just by adding the following css: .mu-emoji { display: none }

This customizations may be chosen from profile view.

[luchotc]

• delete account
• accessibility options like capitalizing all texts

[flbulgarelli]

Also selective user-wise activation of game mode may be a non-visual-only preference.

As stated in this comment, I think we should reify this concept into a preference object:

user.preferences.gamified?
user.preferences.emojiless?
user.preferences.dark?
user.preferences.uppercase?

We could use the composed_of helper like with submissions https://github.com/mumuki/mumuki-domain/blob/abc1ba74a9faf012b7fa225b60c295fe8fc702da/app/models/concerns/contextualization.rb#L25

[felipecalvo]

A downside of using .mu-emoji { display: none } is some (missing) emojis will make the spacing/kerning look a tiny bit wrong:

---

This is minute, I know :smiley:

[flbulgarelli]

Related to https://github.com/mumuki/mumuki-laboratory/issues/472