feat: Export downloadBlob function

In preparation for being able to download the Scratch program in
experience-cs from outside of scratch-gui.

Co-authored-by: Chris Lowis <chris.lowis@gofreerange.com>
Co-authored-by: James Mead <james.mead@gofreerange.com>

Author: 3 people

src/index.js

@@ -7,6 +7,7 @@ import {setFullScreen, setPlayer} from './reducers/mode';
 import {manualUpdateProject, remixProject} from './reducers/project-state';
 import {setAppElement} from 'react-modal';
 import {activateDeck} from './reducers/cards.js';
+import downloadBlob from './lib/download-blob';
 
 const guiReducers = {
     locales: LocalesReducer,
@@ -18,6 +19,7 @@ export {
     GUI as default,
     AppStateHOC,
     setAppElement,
+    downloadBlob,
     guiReducers,
     guiInitialState,
     guiMiddleware,