Remove callbackMesh geometry and material in DropInViewer.dispose

[vincentfretin]

Remove callbackMesh geometry and material in DropInViewer.dispose, that callbackMesh is created in init but never disposed.

I tested it as follow, edit demo/dropin.html to add the two lines to dispose after 10s

viewer.callbackMesh.material.addEventListener('dispose', () => { console.log("disposed"); });
setTimeout(() => { threeScene.remove(viewer); viewer.dispose(); }, 10000);

npm run build
npm run demo

Go to http://localhost:8080/dropin.html
the console.log doesn't show up.

I did the change in src/DropInViewer.js

npm run build
npm run demo

Refresh http://localhost:8080/dropin.html
the console.log disposed shows up.

[hirako2000]

Are PR getting merged once a while ?