Ensure asset serving is portable

Fixes #3094

* Ensure fingerprinting works on Windows
* Removed some tests from versioned assets because these are now
  explicitly tested with a generated reverse router in the
  routes-compiler-plugin scripted tests.
* Made a few stylistic changes (mainly because IntelliJ was marking it
  as a warning).
Merge pull request #3104 from jroper/3094-assets-windows

Ensure asset serving is portable