VTXNORMS chunk for ActorX (vertex normals)

[floxay]

Blender plugins that support this chunk:

• blender3d_import_psk_psa by Befzz (Vertex normals, VTXNORMS chunk Befzz/blender3d_import_psk_psa#69)
• io_scene_psk_psa by DarklightGames (PSKX import functionality DarklightGames/io_scene_psk_psa#17)

[gildor2]

This won't work with Unreal engine itself. The code in UE3 doesn't check chunk names, it just assumes particular chunk order. So, new chunks should be always added to the end.

[cmbasnett]

@gildor2 Can this be merged now? The required fix has been made and I've been using this for the last year or so on my own fork and it works fine.