Add DeprecatedGroup and ObsoleteGroup implementations with unit tests

[wrtobin]

Just putting this up for review for the moment, not married to any design decisions and I assume we'll want to change output message structure.

This basically just introduces mechanisms to lifecycle internal types that have been replaced/supplanted while informing the user in obvious ways and maintaining the schema generation/documentation and parse>init process for that type until it drops completely from the project.

To deprecate any Group subclass just, for e.g. class Foo : public ExecutableGroup (inherits from any group subclass):

class Foo : public DeprecatedGroup< ExecutableGroup >

It basically just injects itself into the inheritance hierarchy and adds the deprecation/obsolescence behavior.