Extract scene functions to their respective modules (#208)

- Also, extract utilities into utils module -- capitalizeString, getDateTime, isInputLike

src/scene/createScene.ts

@@ -0,0 +1,6 @@
+import { ExcalidrawElement } from "../element/types";
+
+export const createScene = () => {
+  const elements = Array.of<ExcalidrawElement>();
+  return { elements };
+};