Rename Space Gray.css to Space_Gray.css

Space_Gray_theme/css/themes/Space Gray.css → Space_Gray_theme/css/themes/Space_Gray.css

@@ -28,4 +28,4 @@
   --calendar-movie-missing: #ff7676;
   --calendar-movie-available: #53e69d;
   --calendar-movie-unreleased: #eeeeee;
-  }
+  }