removed all dependence on NodeOutputs

If Nodes only have the one output, we don't need to do so much differentiation
between them. Previous iteration used outputs as like a distinct function
within a Node (e.g. length output would return one result, buffer output would
produce a different result - each run different code to produce their results).
Now in this iteration, it's more accurate to say a Node is just one function
(which seems more appropriate for a node system anyway).

app/render/backend/renderbackend.cpp

@@ -217,7 +217,7 @@ bool RenderBackend::GenerateData(const TimeRange &range)
     return false;
   }
 
-  NodeDependency dep = NodeDependency(GetDependentInput()->get_connected_output(), range.in(), range.out());
+  NodeDependency dep = NodeDependency(GetDependentInput()->get_connected_node(), range.in(), range.out());
 
   foreach (RenderWorker* worker, processors_) {
     if (worker->IsAvailable() || worker == processors_.last()) {