Add support for http proxies?

[mehaase]

This container only supports socks proxies, but it would be handy to have the option to build it with http proxies instead, similar to https://github.com/mattes/rotating-proxy.

It doesn't seem possible to use HAProxy for that (i.e. set the frontend to http and the backend to tcp: it errors out).The project linked above uses polipo, which is unmaintained. I'm not sure what the best solution here would be.