See https://github.com/nuxeo/nuxeo-drive/issues/30
Need to make sure we are compatible with V1 behaviour:
- 3 possible configurations: System (use system proxy settings, should work on Windows and OS X), Manual, None.
- Handle HTTP and HTTPS protocols
- Use of a dedicated port
- Allow authenticated proxy in case of manual mode
- Handle server exceptions (list of comma separated servers, typically: localhost, 127.0.0.1)