Extract scene functions to their respective modules (#208)

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

src/scene/types.ts

@@ -1,6 +1,12 @@
+import { ExcalidrawTextElement } from "../element/types";
+
 export type SceneState = {
   scrollX: number;
   scrollY: number;
   // null indicates transparent bg
   viewBackgroundColor: string | null;
 };
+
+export interface Scene {
+  elements: ExcalidrawTextElement[];
+}