Add Windows 7&8 and provide http proxy authentication

- I've been testing manually on 7 and 8 for some time. Since both come with powershell, I'd say it's safe to support them
- I've added support for http proxies which require authentication.
- http proxies with authentication tend to carry a lot of security vulnerabilities with plaintext password storage (even firefox). I've mentioned these in the documentation and designed it in a manner that attempts to mitigate these vulnerabilities and properly communicate them to users.