Proxy support

[chriskvik]

Many corporate environments use proxies. As far as I can see proxies are never passed to axios, since this probably is a multi-platform plugin I would suggest to let the user optionally supply a proxy via vscode settings. I dont know if it's possible to get this from the Electron app itself, (most plugins I have tried respects my system proxy).

Or just default to http_proxy or https_proxy env-vars.