Support customizable Service Retirement strategies

Allow the user to specify a set of actions that should be taken when retiring a service version. If no actions are specified, the service is simply removed from the Gateway immediately and all applications using it are out of luck. Actions that can be taken may include:

• Reduce all usage limits but otherwise respond normally
• After 30 days respond with http 410 (Gone)
• After 60 days remove entirely (gateway will start returning 404 Not Found)

Other retirement strategy actions may be to auto-redirect to the new service version, etc...

See discussion here: https://community.jboss.org/message/880935#880935