Ability to download files

[GoogleCodeExporter]

This is probably the only thing missing in phpdesktop right now, that would 
prevent existing web apps from working out of the box. This still needs work. 
We would need to implement CefDownoadHandler and display some "Save as" dialog 
using Windows API call, probably GetSaveFileName():

http://msdn.microsoft.com/en-us/library/windows/desktop/ms646928(v=vs.85).aspx

It would be nice to have the "Save as" in mouse context menu that would appear 
for links. It would give ability to download even those files that are not 
normally downloadable (no headers that identify it as an attachment).

I'm not yet completely sure about the "Save as" feature in context menu. How 
should it behave when user tries to download a link that is an html page? I 
don't think I'm going to implement the "Save complete webpage" feature, it's 
much more work, and it feels like it's a feature for a real web browser.

What would be the use cases for the "Save as" feature? I'm not yet convinced 
that we really need it. It would definitely need to be configurable through the 
settings.json file, because it's probably not desirable by everyone.

Original issue reported on code.google.com by [email protected] on 23 Jan 2014 at 6:55