Add import/export of CULL zones from/to IPL

[Psycrow101]

Add the feature to import CULL zones from IPL for GTA III/VC/SA games and export back to text format

Wiki info: https://web.archive.org/web/20241220003451/https://gtamods.com/wiki/CULL

CULL zones should be made as a separate object type as a cube primitive. When importing IPL cull objects are placed in a separate collection. Work with CULL zones should be made similar to work with collisions