move sticker questions to backend

[akhrail1996]

probably we can start with this:
return categories (questions with icon URLs) and corresponding options (sticker-based URLs and text-based) on profileChannel.join

[ruslandoga]

I probably would start on it after new-socket is merged and used on ios, so the approach would likely be different.

[akhrail1996]

@ruslandoga agree
we probably won't forget about this issue anyways, but maybe better to keep it open (since it's an actual issue) with some label indicating it being blocked (to start building the right github / project development habits).
What do you think?