added convenience functions for working with NodeInputArray

NodeInputArray has to work a certain way internally, but it can still provide
array-like convenience functions to the rest of the program.

app/node/inputarray.h

@@ -5,13 +5,25 @@
 
 class NodeInputArray : public NodeInput
 {
+  Q_OBJECT
 public:
   NodeInputArray(const QString &id);
 
   int GetSize() const;
+
+  void Prepend();
+  void Append();
+  void InsertAt(int index);
+  void RemoveLast();
+  void RemoveAt(int index);
   void SetSize(int size);
 
-  NodeInput* ParamAt(int index);
+  int IndexOfSubParameter(NodeInput* input) const;
+
+  NodeInput* ParamAt(int index) const;
+
+signals:
+  void SizeChanged(int size);
 
 private:
   QVector<NodeInput*> sub_params_;