Add DLC YTYP requests; update map stream

Add two data_file 'DLC_ITYP_REQUEST' entries to fxmanifest to load stream/bzzz_scrap_items.ytyp and stream/pnwsigns.ytyp so those prop types are available to the map. Also update the SandyMotelConstruction.ymap in the stream (binary change). No other script changes.
