Extract "dx get applet-XXXX" machinery into its own module.
Move app_unbuilder module to dxpy.utils.
dxpy/dx workflow minor improvements

- Bug fix for handling init_from/--init correctly
- Formatted describe output for initializedFrom
- Additional test coverage
Upgrade setuptools dependency from 1.1.6 to 2.1
Disable dxpy client-side retry heuristic