Asset viewer for engines

[allenz-crypto]

The new asset viewer feature does not seem to work for engines.

I have several svg files inside the public folder of an Ember engine, but when I launch http://localhost:4200/ember-svg-jar/index.html from the engine, it shows my assets library as empty.

[voltidev]

Unfortunately, I don't have time to add engines support for the asset viewer. Feel free to make a PR if you have a chance.