Bundle ios_webkit_debug_proxy for OS X. Fixes #37.

This includes the iOS proxy into the add-on for OS X.

The process to start things like iOS from WebIDE is still crazy, but I'm actively fixing up how the WebIDE API to this add-on separately.
Not terribly relevant to this patch, but I wonder if the add-on still runs on 33.  There were a number of times that we had to update due to breakage induced from Firefox changes and that might affect the compatibility claims we can make here.