feature_request: option to use named keys for caching

[tkmmark]

Consider allowing user to supplement their own named keys when caching object... in order to facilitate more intuitive retrieval of cached objects. This involves making the following changes:

(1) Create property in ServerProtocol class to store the map between datakey and id:_

(2) Inside the Proxy class..._
When a user supply a datakey, this is sent along with the data to the server

(3) Correspondingly, the ServerProtocol class stores any supplied datakey to the property / mapper described in (1)

(4) In the Get method of the ServerProtocol class, allow the datakey to be used for retrieving cached object... (If the key is not an ID, the method will search for stored keys)

[tkmmark]

And it would be nice to also to add a method to allow users to see what datakeys have already been added...
The required changes for the process() in the ServerProtocol is captured in the screenshot below: