Add the ability to handle nested actors, launching, stopping, indexing and invalidating.

A derived actor class can add nested actors, launch and stop them by name, and handle their last acknoweldge. The CSPP_BaseActor will send a warning to the message handler if nested actor is unexpectetly stopped, meaning not handled by derived class. CSPP_BaseActor will stop nested actors at the end of its life cycle in any case.

CSPP_Core-errors.txt

@@ -73,7 +73,7 @@ Custom serial parameter not supported.
 Actor Name is unknown within the specific application.
 </nierror>
 <nierror code="-8979">
-Emty message name.
+Empty message name.
 </nierror>
 <nierror code="-8978">
 PV data type not supported.
@@ -88,4 +88,6 @@ Priority message queue pile-up monitoring not enabled.
 <nierror code="-8975">
 QMessageLogger: Queue already exists.
 </nierror>
+<nierror code="-8974">
+Empty nested actor name.
 </nidocument>
\ No newline at end of file