Added GUI elements: loading scene with menu, boost indicator

to view the "menu" screen, load the "LoadScreen" scene and hit play. Then hit the "Load demo scene" button to launch the shootingdemo scene. This requires that both scenes are present and numbered in the build settings dialog (LoadScreen should be level 0, shootingdemo should be level 1). Hopefully, including my changes to ProjectSettings/EditorBuildSettings.asset should have made these changes automatically, but not sure.