Plugin Discovery Revamp & Re-organization.

General: Organizes tests into API and CLI directories.
CLI: Moves bin/sl code to SoftLayer/CLI/__init__.py for 2to3 and testability.
CLI: Instead of the 'scripts' directive in setup.py the script is now installed via
     the 'entry_points' argument. See: http://stackoverflow.com/a/17933
CLI: Adds tests for all functions migrated from bin/sl except for main()
CLI: Revamps how module discovery works. Importing a class that inherits
     CLIRunnable will not register itself to SoftLayer.CLI.plugins.
     e.g.: {'cci': {'list': ListCCIs}}
CLI: Python 3 compatability for the CLI???