Feature/user_service

[rahulj123atwork]

Enhanced support for softlayer_user_customer resource, as needed by Terraform library.

• Added fields to SoftLayer_User_Customer type. Defined new types for user permissions, and user delete.
• Implemented CreateObject(), GetObject(), EditObject(), DeleteObject()
• Implement RemoveApiAuthenticationKey()
• Implemented AddBulkPortalPermission(), RemoveBulkPortalPermission(), GetPermissions()
• Added unit tests for each of the above APIs along with the necessary test_fixtures.

[renier]

Rebased this branch on top of sl-dev.