Feature request: OpenBazaar-client proxy support

[gndgnd]

Hi,

i would be interested to use the client together with a proxy. If the server is not on the same machine and is remote, OpenBazaar client should have an option to configure a proxy server.

This is useful for several situation:
1. Increased server security: if the proxy server has a fixed IP, only that IP can be allowed to connect to OpenBazaar server, whereas the client might roam around freely
2. Increased server security: if the proxy server is the same as the OpenBazaar server, there is no need to expose the port(s) to the outside
3. Better security for the client - the client is able to hide its real IP
4. Better overall experience: for users with clients behind restrictive firewalls, etc..

Couldnt find anything proxy-related in the issues or code, so i add this as a feature request. I guess its one that is fairly easy to implement. Thank you for considering it !