Prepare for ProxyCommand support
Mockup
Gray proxy Username/Password label when controlled disabled
Add initial support for ProxyCommand
Update connect.c from https://bitbucket.org/gotoh/connect/raw/tip/connect.c
Add "HTTP_PROXY_FORCE_AUTH" env var to force send authentication, for some http proxy do not support negotiate auth (ie. Polipo)
Support connecting through SOCKS v5 / SOCKS v4 / HTTP proxy with authentication