Move images used in posts to assets directory

[Robyt3]

Supersedes #332.

[heinrich5991]

AFAICT, this unnecessarily creates dead links (to images, possibly linked from outside DDNet). Unless we find a way to prevent this, I'd like to revert this PR.

[Robyt3]

We can probably create redirects, but I don't know how to do this with our web server. Here is a list of all moved files extracted from the patch:

2_To_Tango.png
7thbirthday2.png
Arctic_Frost.png
Behemoth_2.png
Best_of_Three.png
birthday3.png
Bollermann.png
brainduck2.png
buggy-tiles-discord.png
CareForYourTime.png
Chill_Let_s_Climb_3.png
code-changes.png
ddnet-to-greenlight.svg
DEATHBOW.png
discord_info.png
discord_records.png
Fall_into_the_Future.png
finishes-10000000.png
fundingsecured2022.png
fundingsecured2023.png
fundingsecured2025.png
Gedan.png
halloween.png
JustGeneric.png
Knux.png
luminati.png
map_profile_Cuboid.png
most-finishes.png
Moventer.png
Naufrage_4.png
newyear.png
newyear2022.jpg
newyear2023.jpg
newyear2024.jpg
newyear2025.jpg
Noovice!.png
Not_Naufrage_4.png
Patchwork.png
player-activity.png
playersannotated.png
points-earned.png
profile_Starkiller.png
Shockwave.png
Shooting_Range.png
Simple_Down.png
solo-cheat.png
Squidgy.png
steambeta1.png
steambeta2.png
steamcategory.png
swap_cheat.mp4
Teetrader.png
Tutorial.png
UpNDown_Coop.png
videorecorder.png
ZooDrag.png

[heinrich5991]

Perhaps we could add symlinks for these redirects to the git repository?

[Robyt3]

Perhaps we could add symlinks for these redirects to the git repository?

I'd prefer not having all of the file/symlink entries in the www folder.