There was a case with the hashed-password which had multiple equal signs in the
value and it wasn't being parsed correctly. This uses a new function and adds a
few tests.

Unfortunately since plugins can now override the root this is necessary
or just can't log in.

This will let them throw and show nice errors more easily.

This is mainly so they can get relative paths in their HTML, in
particular code-server's static base so they can use the favicon and
service worker.

So plugins can pass the logger around.

Same reasoning used when exposing Express.

In case they need to map it to something else.

Makes typing much easier. Addresse's Will's last comment.

Next commit will address Will's comments about the typings being weird.

More clear.

See my discussion with Will in the PR.