assault rifle world model optimisation
- combined the 4 part FBXs into one model and converted the LOD group to a MeshLOD
- renderers 12 -> 1, highlight draws 4 -> 1, triangles unchanged, culls at 35m
- combined the ak47u's 4 part FBXs and the medieval's rifle+mag into single models
- converted the ak47u, medieval and jungle world models from LOD groups to MeshLODs
- removed the medieval's 23.6k tri LOD0 - its chain is now 13k/5.3k/2.1k
- renderers: ak47u 12 -> 1, medieval 8 -> 1, jungle 3 -> 1; highlight draws all down to 1