new stager reverse_http_proxy_pstore

This does the same as windows stager reverse_http but it also tries to obtain authentication from Windows Protected Storage (used in Win XP and Win Server 2003, IE Version 4 to 6) and passes them to the preconfigured proxy server via InternetConnect function.

If no authentication is found or there is no preconfigured proxy server, this should work just like reverse_http.
This doesn't need to prevent this from landing @jlee-r7 as it's more a refactor of existing modules?