Lighting LOD

Lighting billboard LOD:

Almost all lighting billboards come from OBJs, via named lights or custom lights.

They are usually subject to LOD. However, there are some exceptions.

Philosophy:
 * Authors know better than x-plane when an OBJ should disappear - it's a subjective thing. X-Plane always honors ATTR_LOD for triangles.
 * X-Plane knows better than authors when a light should disappear - since X-Plane knows how those abstract light params are rendered. X-Plane may ignore LOD.  Usually this involves light being drawn for a longer distance, in cases where there is no perf hit in the rendering enigne.  This is almost always desirable for authors.

Guidelines:
 * Replicate your lights through all LODs with the SAME exact values.
 * You can drop a light in far LOD but don't add one.

Notes on implementation:
 * X-Plane may draw your light for longer than you want - calc will be based on light's actual appearance.
 * X-Plane won't double-draw extended-LOD lights when repeated in two LODs. Not a problem!
 * Don't add lights in far LOD - X-Plane may not be able to accurately do this effect if it is tampering with LOD!
 * If your last LOD is light only, X-Plane can handle this VERY efficiently. So often there is penalty for huge final LOD for a named light that is geo only.