Misc OSX porting things:

* autostart the assistant on OSX, using launchd
* add webapp to OSX menu somehow
* Use OSX's "network reachability functionality" to detect when on a network
  <http://developer.apple.com/library/mac/#documentation/Networking/Conceptual/SystemConfigFrameworks/SC_Intro/SC_Intro.html#//apple_ref/doc/uid/TP40001065>