LWOloader: lwo3 IFF-parsing types fix

[sciecode]

Follow up on #16117

parsing type fix.
case insensitive /images textures path.
surfaces sub-chunk DIFF extension to lwo3 format.

[looeee]

case insensitive /images textures path.

That's fine, but the reason that it's Images with capital I is because that's the way Lightwave sets up the project folder. It will always be:

-> Project Dir
--> Images
--> Objects

Images will have texture files, and Objects will have .LWO files.
If you reference textures from outside Images in Lightwave, it stores the absolute path in the LWO file: d:/some_dir/texture/image.png.

[mrdoob]

Thanks!