API: Settings are now loaded from config files

Now when SoftLayer.Client() is called it will check for settings in this order:
 * User-Supplied Arguments
 * Environmental Variables
 * User-supplied config file, ~/softlayer, /etc/softlayer.conf

Once the configuration reaches a username and api_key it will stop gathering settings and use the settings it has thus far.

API: Removes the use of globals for configuring the API client.
CLI: Lots of config logic was taken out of the CLI so it could leverage the API configuration that happens automatically.