Provide platform icons for each OS

The platform does't have a specific icon, so the Javaicon is displayed for the nuxeo launcher.
http://iconhandbook.co.uk/reference/chart/windows/

Default format and size for OS X, Windows 7 / 8:
https://developer.apple.com/library/mac/DOCUMENTATION/UserExperience/Conceptual/AppleHIGuidelines/IconsImages/IconsImages.html
http://stackoverflow.com/questions/3236115/which-icon-sizes-should-my-windows-applications-icon-include