Save images offline, in the snapshot (#770)

* Implemented image restore from rr_dataURL

* Implement saving images in the snapshot

* Fixed image saving, added a test

* Rename data-src to data-rrweb-src

* Updated the guide

* Rename recordImages to inlineImages and try catch

packages/rrweb-snapshot/test/__snapshots__/integration.test.ts.snap

@@ -326,6 +326,7 @@ exports[`integration tests [html file]: picture.html 1`] = `
       <source type=\\"image/webp\\" srcset=\\"http://localhost:3030/assets/img/characters/robot.webp\\" />
       <img src=\\"http://localhost:3030/assets/img/characters/robot.png\\" />
     </picture>
+    <img src=\\"http://localhost:3030/images/robot.png\\" alt=\\"This is a robot\\" />
   </body></html>"
 `;