OS X Support

The os x installation and running now fully works.

Have tested:

* successful install
* quitting an install mid-way through (we could enhance this by deleting the application bundle in ~/Applications?)
* opening multiple builders from the website

This branch has allowed us to:

* remove the need for applescript (yay!)
* have native python that listens for osx url/file events
* have consistent icons (including windows/linux)