WIP: Windows Server CI

[JohnMcLear]

Due to #4787 it's clear we need some CI for running Etherpad Server on Windows server and run some backend tests(no need for frontend).

Todo:

• Fix 4787
• Test if mocha timeouts are long enough
• Test runner
• Fix tests that fail in Windows importExportGetPost.js <-- they don't fail on my local windows machine! 🍡
• Revert 306390c
• Fiesta

[JohnMcLear]

Note that before this is merged the removal of tests should be taken back out, they are removed to make testing the PR easier.

mocha --timeout 120000 --recursive tests/backend/specs ../node_modules/ep_*/static/tests/backend/specs from runBackendTests.sh or whatever might not be a long timeout because the test runner starts at the same time as the node process (intentional).

Once the windows build is fixed we can finish this PR off.