created NodeInputArray parameter type

It seems unwise to let NodeInputs take more than one value, but at times
it makes sense to create a list or array of inputs. This class will create
sub-parameters as an easy way to provide variable inputs while also enforcing
one connection per input parameter.

This is also the primary motivation for the previous commit (disambiguating
when a NodeParam's parent is a Node vs some other type).

app/node/inputarray.h

@@ -1,11 +1,21 @@
 #ifndef INPUTARRAY_H
 #define INPUTARRAY_H
 
+#include "input.h"
 
-class InputArray
+class NodeInputArray : public NodeInput
 {
 public:
-  InputArray();
+  NodeInputArray(const QString &id);
+
+  int GetSize() const;
+  void SetSize(int size);
+
+  NodeInput* ParamAt(int index);
+
+private:
+  QVector<NodeInput*> sub_params_;
+
 };
 
 #endif // INPUTARRAY_H