WIP Added ability to provide a collection of configuration system prefixes for a CornerstoneConfigurable.

Change-Id: Ie7b062d0ccaf07b6832fd661a96e915cbe324243
CornerstoneConfigurable is no longer abstract.

There was nothing in its design that requires a subclass, and use cases have emerged for
using instances of it directly.

Change-Id: I8871e8f89415744ccb455b3befb2c3eb22bd99a7