Fix Medium Generic Windowed House Style 3 not deploying

The shared building template for the Style 3 windowed medium house was
missing the appearanceFilename field. The s01 and s02 variants both
define this field (pointing to their respective _r0_exterior.apt files),
which the structure placement system uses to render the exterior preview
when a player attempts to place the building. Without it, the placement
HUD silently fails and nothing happens when the deed is used.

Added appearanceFilename following the naming convention established by
the s03 portal layout file (ply_house_med_s03_hue.pob).

Fixes #276

Author: nickk02

sku.0/sys.shared/compiled/game/object/building/player/shared_player_house_generic_medium_windowed_s03.tpf

@@ -16,6 +16,8 @@ clearFloraRadius = 38
 objectName = "building_name" "player_house_generic_medium_windowed_s03"
 detailedDescription = "building_detail" "player_house_generic_medium_windowed_s03"
 
+appearanceFilename = "appearance/ply_house_med_s03_hue_r0_exterior.apt"
+
 portalLayoutFilename = "appearance/ply_house_med_s03_hue.pob"
 
 clientDataFile = "clientdata/building/shared_player_house_tatooine_medium_style_01.cdf"