Add proxy support

The Installer has issues when I'm behind our corporate proxy.

I haven't found network settings in C:\Users\<Profile>\AppData\Roaming\installer\preferences.

[mikeal]

Is your corporate proxy blocking calls to nodejs.org?

No blocking, nodejs.org works when browsing in Chrome or Firefox.

In my .npmrc file I have the proxy configured, npm works. NI doesn't.

[mikeal]

Oh i see, the proxy has to be configured. There has to be a module to pull the globally configured proxy setting. Once we pull that we can easily use it in request.