ISPN-5013 Stored Script Execution 

https://issues.jboss.org/browse/ISPN-5013

WARNING: this is merely a preview of stored script execution. Please contribute to the design doc:
https://github.com/infinispan/infinispan/wiki/Script-Execution-Design
and obviously comment on the code here.
@tristantarrant is this something that will be worked on a bit later?