[CDN] Unscrew filesystem layout (CDN)

[TheArcaneBrony]

A bunch of CDN endpoints are currently writing into /avatars, when they should be their own storage directories:

• /icons/
• /emojis/
• /stickers/
• /banners/
• /splashes/
• /discovery-splashes/
• /app-icons/
• /app-assets/
• /discover-splashes/
• /team-icons/
• /channel-icons/

[TheArcaneBrony]

NOTE: this should probably be an opt in thing or have some temporary fallback behavior to /avatars until #1453 is resolved?

[MathMan05]

Or maybe a try the correct dir and fallback to avatars type thing

[TheArcaneBrony]

I already mentioned that if you re-read my comment :P