Fix map files for frontend resources

[jandd]

Only issue is: when I ran this locally and checked the start page, everything looked fine. But when I further inspected the developer console I got the following error:

Failed to load resource: the server responded with a status of 404 (Not Found) http://0.0.0.0:8000/static/js/bootstrap.js.map

This won't break functionality, but might be a regression.

Originally posted by @jenslauterbach in #295 (review)