Make tests self-hosting

* Add wptserve as a submodule for serving HTTP files

* Add pywebsocket as a submodule for websockets

* Add a serve.py script that initalises the test environment
  with the servers running on free ports

* Remove all PHP from the repository and replace it with
  wptserve-compatible python

* Remove all .htaccess files from the repository and replace
  with .headers files

* Some additional fixes to tests that were otherwise broken

* Add bugs to tests (probably) that need to be identified and
  fixed in followup commits.
fixup! Make tests self-hosting
fixup! Make tests self-hosting

Fix review issues in CORS and Event-Source
Update wptserve version
Update wptserve version
Update wptserve version
EventSource CORS: Fix buggy test
Fix more review issues
Fix more review issues
Fix templates test
request.GET needs either [] or an explicit method
Update to latest wptserve
Add some missing files
Change default delay to 500ms, not 500µs
Stray 'PHP-semicolon'
Update to latest testharness.js
Add some documentation for writing complex tests
fixup! Add some documentation for writing complex tests
Update use of headers.append
Typos