- Use command-line flags instead of a config file, ensuring we always
  have the required options set.
- Allow for a BASE_PATH environment variable for when you are proxying
  code-server with a base path which code-server can then pass along to
  Jupyter.

Jupyter support

The problem is that you might click multiple times if it appears to be a
bit slow and get multiple processes running. This will also pave the way
for processes that you want to reuse (like Jupyter).

Just needed to properly listen for the ready message since other
messages might get through while reconnecting.

HTTP proxy

Otherwise the request will just hang.

Also fixed a type issue.

The raw value is now passed back to VS Code so it can do the parsing
with its own URI class rather than trying to parse using Node's url
module first since that has no guarantee of working the same way. It
also lets us keep the vscode-remote bit internal to VS Code.

Removed the logic that keeps trying paths until it finds a valid one
because it seems confusing to open a path and silently get some other
path instead of an error for the one you tried to open. Now it'll just
use exactly what you specified or fail trying.

Fixes #1488. The problem here was that url.parse was encoding the spaces
then the validation failed looking for a literal %20.

Send report issues to code-server repo

Back up old directory when updating

This makes the code much more internally consistent (providers just
return payloads, include the proxy provider).

There's no need to specially construct the path.