294 LOD Property Rules

2.49 LOD properties have some special rules for their use

1. LOD property names match "LOD_[0123]" and are not case sensitive
2. 0 or more LOD property names can be defined
3. In 2.49 LODs are gathered (for some awful reason and in an awfully stateful way) in XPlaneExport.getTextures. LOD properties can be defined on any of the objects in the search space, and be applied to the destination XPlaneLayer
4. In 2.49 Additive LOD mode is set by an "additive_lod" property somewhere in the search space
5. Any use of LOD properties writes any applicable them to the file. Therefore, if we don't encounter LOD properties, we shouldn't apply them
6. There is an exception: If there are objects on layer 2 or 3 and there are no LODs, use the default LODs

We copy this behavior as is