feat: include an option to use a proxy

[GabrielGil]

I am opening this issue because I think an option to use a proxy on the app would really add more value to use the app over using just the browser.

Google Play Music is not available in many countries yet, so using a proxy is the only option for these places.

I am aware that enabling the proxy system wide would just work but it has downsides.

[noizo]

And in some corpo networks, folks are still blocking youtube music on network level. Proxy would help to solve that (SOCKS4,5, with password authentication in my case)