decouple freeing shared and model objects from the synth with PlugInCmd

This should give much stronger guarantees that the server and client 
agree about what exists. It would be neat if the server could delete its 
own node as well, but I haven't worked out how to do this yet

include/FluidSCWrapper.hpp

@@ -586,13 +586,16 @@ struct LifetimePolicy<Client, Wrapper,std::true_type, std::false_type>
 
   static void setup(InterfaceTable* ft, const char* name)
   {
-      ft->fDefineUnitCmd(name, "free", [](Unit* unit, sc_msg_iter*)
-      {
-        //This ABSOLUTELY ASSUMES the client is going to also delete
-        //the Unit by calling Synth.free.
-        auto wrapper = static_cast<Wrapper*>(unit);
-        mRegistry.erase(wrapper->uid);
-      });
+      auto freeName = std::stringstream();
+      freeName << "free" << name;
+    
+      ft->fDefinePlugInCmd(freeName.str().c_str(),
+       [](World*,void*,sc_msg_iter* args, void*/*replyAddr*/)
+       {
+          auto objectID = args->geti();
+          auto pos = mRegistry.find(objectID);
+          if(pos != mRegistry.end()) mRegistry.erase(objectID);
+       }, &mRegistry);
   }
 
 private:
@@ -641,12 +644,19 @@ struct LifetimePolicy<Client, Wrapper,std::false_type, std::true_type>
 
   static void setup(InterfaceTable* ft, const char* name)
   {
-      ft->fDefineUnitCmd(name, "free", [](Unit* unit, sc_msg_iter*)
-      {
-          auto clientRef = getClientPointer(static_cast<Wrapper*>(unit));
+
+      auto freeName = std::stringstream();
+      freeName << "free" << name;
+    
+      ft->fDefinePlugInCmd(freeName.str().c_str(),
+       [](World*,void*,sc_msg_iter* args, void* /*replyAddr*/)
+       {
+          auto objectName = std::string(args->gets());
+          auto clientRef = SharedType::lookup(objectName);
           auto pos = mRegistry.find(clientRef);
           if(pos != mRegistry.end()) mRegistry.erase(clientRef);
-      });
+       }, &mRegistry);
+    
   }
 private:
   static  ClientPointer getClientPointer(Wrapper* wrapper)