Running X11 applications on MacOSX

[tomzo]

Some dojo images with graphical apps could be executed on Mac.

I've just made a few experiments with running X11 over Quartz as described on https://gist.github.com/tomzo/9b8c906289c7959ffc01eea988b17d89#proxying

The setup steps needed before X11 proxying is running are a bit long. We should think on how much of it should be a part of dojo (if at all).