Simplified http proxy for cross domain requests. Should help #175 and #7...

Hi,

I had some problems with the proxing, and was reading #74 and [#175](https://github.com/phonegap/phonegap-app-developer/issues/175), and decided to send you guys a PR to make the http-proxy a little simplier.

This uses node-http-proxy to handle the proxing and rewrites the location header in case the target sends one. 
This way if the 'api backend' responds a redirect, the browser follow it.. :)

Also it does not mess up with the body building, which was the problem in my use-case.

Happy new year!