Implement Save without re-prompt and Save as (#1709)

* Implement Save without re-prompt and Save as
Fixes #1668

* Add save-as icon

* Make .excalidraw the default extension

* Only show save as button on supporting browsers

src/actions/index.ts

@@ -34,6 +34,7 @@ export {
   actionChangeProjectName,
   actionChangeExportBackground,
   actionSaveScene,
+  actionSaveAsScene,
   actionLoadScene,
 } from "./actionExport";