The Gaudi PluginSvc has been refactored and modernizes.
See gaudi/Gaudi!709

As well as some changes to macros that directly call on
certain features of the PluginSvc itself, other code that
has been impacted is as follows:

 - destructors of Converters must be public
 - template arguments of ServiceHandles and ToolHandles cannot always be forward defined and the associated header files may need to be explicitly included


Former-commit-id: 83042516db016cf1ec8fde0d4dca19a2cdaa5e79