Make the app downloadable as a zip

[adrianschmidt]

I'm submitting a ... (check one with "x")
[ ] bug report
[x] feature request
[ ] support request

Some users will want to download the app as a zip-file to ensure they have access to it for perpetuity. While the source-code is already downloadable, this isn't very helpful to non-programmers.

The easiest way might be to use relative paths for all internal references. That way, the build-output should be usable by simply opening the index.html file in a browser, without even using a web-server.