ResultCache impl for extensions of DataConnector

[Rod Widdowson]

> Likewise I believe all the logic that would make it easy to support XML configuration is also not API, unfortunately, but there's
a class
> called CacheConfigParser that does all that.

Actually AbstractDataConnector was moved out of impl in a recent release.

I'd be interested in any suggestions of classes to move oout from API, possible as part of IDP-1179.  We know that we started of
quite conservatively with API classes during V3, but now we have more experiences we can make changes.

Rod