refactor(showcase): replaced Unreal ContentExampleUAssets with selfmade UAssets.

Content/ContentExamples/DemoRoomUAssets/BP_DemoRoom.uasset

...ent/ContentExamples/DemoRoomUAssets/BP_Demostation.uasset

Content/ContentExamples/DemoRoomUAssets/DemoRoom.uasset

...xamples/DemoRoomUAssets/DemoRoomAssets_back_piller.uasset

...tExamples/DemoRoomUAssets/DemoRoomAssets_connector.uasset

...ntentExamples/DemoRoomUAssets/DemoRoomAssets_floor.uasset

...amples/DemoRoomUAssets/DemoRoomAssets_front_pillar.uasset

...tExamples/DemoRoomUAssets/DemoRoomAssets_long_wall.uasset

...Examples/DemoRoomUAssets/DemoRoomAssets_short_wall.uasset

...DemoRoomUAssets/DemoRoomAssets_vertical_end_piller.uasset

Content/ContentExamples/DemoRoomUAssets/DemoRoomTest.umap

...t/ContentExamples/DemoRoomUAssets/Entrance_Pillars.uasset

Content/ContentExamples/DemoRoomUAssets/Floor.uasset

Content/ContentExamples/DemoRoomUAssets/Frame.uasset

Content/ContentExamples/DemoRoomUAssets/Inner_Walls.uasset

Content/ContentExamples/DemoRoomUAssets/Interior.uasset

Content/ContentExamples/DemoRoomUAssets/Outer_Pillars.uasset

Content/ContentExamples/DemoRoomUAssets/Outer_Walls.uasset

...nt/ContentExamples/DemoRoomUAssets/Outer_Walls_007.uasset

...ent/ContentExamples/DemoRoomUAssets/S_RoomSettings.uasset