feat: Add toggle to allow fast type speed

[arthurdenner]

Closes #18.

Within this PR:

• A Toggle component was added to allow fast type speed;
• The Nav component was refactored to be a functional component since we don't have language options yet;
• The same "handle" function is used to update local state and localStorage when a Toggle changes;
• A few styles were changed to better show the toggles;
• The ESLint errors were fixed.

PS: I'm not satisfied with the labels Normal type speedand Fast type speed, but I don't know how to better name them. Suggestions are welcome. :sweat_smile:

Let me know if you want me to undo any change or do something else.

[ade-fatimah]

Oh, nice! This is so lovely! we really appreciate this PR.