Merge upstream PRs

[Archmonger]

Description

Since ServeStatic is a fork of WhiteNoise for continued maintenance, there are a handful of whitenoise PRs that can/should be merged into this repo.

Mergeable as-is

• Fix issue with static files on Windows evansd/whitenoise#474
• Compress each file in a ThreadPool evansd/whitenoise#484

Requires some work

• Nice 404 error message evansd/whitenoise#366
• Added Django Middleware that Delays Traversal of Static Root until Requested evansd/whitenoise#275
  • This might be better implemented as a static manifest file.
  • Maybe only allow this with ManifestStaticFilesStorage?
• Use settings.FORCE_SCRIPT_NAME correctly evansd/whitenoise#486

Probably wont merge

• Add compress skip patterns from settings evansd/whitenoise#297
• Skip compression of already compressed files evansd/whitenoise#347
• Changable compressor class evansd/whitenoise#354
• Test that scantree isn’t run multiple times per test suite evansd/whitenoise#562
• Add type checking with Mypy evansd/whitenoise#410