[Feature Request] Skybox

Add natives to the `NextClientServerApi` that allow setting and restoring a `skybox` for a specific player or for all players in real time.

Suggestion:
```cpp
native ncl_set_skyname(index, const skyName[]);
native ncl_restore_skyname(index);
```
Example usage:
```cpp
ncl_set_skyname(id, "tornsky");
ncl_restore_skyname(id);

ncl_set_skyname(0, "city1");
ncl_restore_skyname(0);
```