[DON'T SUBMIT] Super hacky image embedder (makes maps compatible to 0.7)

[def-]

For #1906

Instructions:

• Copy all maps to ~/.teeworlds/maps
• Open map editor and click on load
• New maps are now in ~/.teeworlds

Initially I tried to use map_replace_image and build something based on that but that turned out to be harder than this approach.

[def-]

Apparently crashes:

[2019-09-16 15:24:41][datafile]: loading data index=1 size=27072 uncompressed=4194304
[2019-09-16 15:24:41][datafile]: loading data index=3 size=5086 uncompressed=120000

Thread 1 "zillywoods" received signal SIGSEGV, Segmentation fault.
__memmove_avx_unaligned_erms () at ../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S:262
262 ../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S: No such file or directory.
(gdb) bt
#0  __memmove_avx_unaligned_erms () at ../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S:262
#1  0x00005555556961d4 in mem_copy (dest=0x5555581c3230, source=0x0, size=262144) at src/base/system.c:300
#2  0x00005555555928bf in CGraphics_Threaded::LoadTextureRaw (this=0x7ffff44c7010, Width=256, Height=256, Format=1, pData=0x0, StoreFormat=1, Flags=0) at src/engine/client/graphics_threaded.cpp:371
#3  0x00005555556197c8 in CMapImages::LoadMapImages (this=0x555555847600 <gs_MapImages>, pMap=0x5555559169e0, pLayers=0x555555918d50, MapType=0) at src/game/client/components/mapimages.cpp:62
#4  0x0000555555619879 in CMapImages::OnMapLoad (this=0x555555847600 <gs_MapImages>) at src/game/client/components/mapimages.cpp:74
#5  0x00005555555b4ffb in CGameClient::OnConnected (this=0x5555559184b0) at src/game/client/gameclient.cpp:413
#6  0x000055555559bc87 in CClient::ProcessServerPacket (this=0x7ffff4e0d010, pPacket=0x7fffffffdcc0) at src/engine/client/client.cpp:1212
#7  0x000055555559cfeb in CClient::PumpNetwork (this=0x7ffff4e0d010) at src/engine/client/client.cpp:1526
#8  0x000055555559d8aa in CClient::Update (this=0x7ffff4e0d010) at src/engine/client/client.cpp:1727
#9  0x000055555559ebb5 in CClient::Run (this=0x7ffff4e0d010) at src/engine/client/client.cpp:2069
#10 0x00005555555a0d21 in main (argc=1, argv=0x7fffffffe078) at src/engine/client/client.cpp:2677

[def-]

Fixed the crash.