copy node graph before rendering

Previous iterations would use mutexes to prevent changing of the graph
mid-render, however several user actions would need to capture these mutexes
causing the main thread to hang until the current render job (frame/range of
samples) was complete. We now copy the nodes necessary as part of the "compile"
process so that the main thread shouldn't need nearly as much blocking while
caching occurs.

app/node/param.cpp

@@ -130,8 +130,8 @@ void NodeParam::DisconnectEdge(NodeEdgePtr edge)
   output->parent()->LockUserInput();
   input->parent()->LockUserInput();
 
-  output->edges_.removeAll(edge);
-  input->edges_.removeAll(edge);
+  output->edges_.removeOne(edge);
+  input->edges_.removeOne(edge);
 
   output->parent()->UnlockUserInput();
   input->parent()->UnlockUserInput();