Improve printing support of Atom Shell

by Haojian Wu for GitHub

The aim of the project is to implement printing features of Atom Shell on Windows as well as add more options allowing user to custom printing settings. Currently, due to the complicated printing code of Chromium on Windows, the printing API(window.print()) only works well on Linux and OS X platforms. The project involves implementing printing features on Windows by porting the printing code of chromium and adding some options in printing feature.