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/node/node.h

@@ -139,7 +139,7 @@ public:
   /**
    * @brief Generate OpenCL hardware accelerated code for this Node
    */
-  virtual QString Code(NodeOutput* output) const;
+  virtual QString Code() const;
 
   /**
    * @brief Returns the parameter with the specified ID (or nullptr if it doesn't exist)
@@ -264,6 +264,8 @@ public:
    */
   bool HasParamWithID(const QString& id) const;
 
+  NodeOutput* output() const;
+
 protected:
   /**
    * @brief Add a parameter to this node
@@ -274,16 +276,6 @@ protected:
    */
   void AddParameter(NodeParam* param);
 
-  /**
-   * @brief Retrieve the last timecode Process() was called with
-   */
-  rational LastProcessedTime();
-
-  /**
-   * @brief Retrieve the last parameter Process() was called from
-   */
-  NodeOutput* LastProcessedOutput();
-
   void ClearCachedValuesInParameters(const rational& start_range, const rational& end_range);
 
   void SendInvalidateCache(const rational& start_range, const rational& end_range);
@@ -320,16 +312,6 @@ private:
 
   QList<NodeParam *> params_;
 
-  /**
-   * @brief The last timecode Process() was called with
-   */
-  rational last_processed_time_;
-
-  /**
-   * @brief The last parameter Process() was called from
-   */
-  NodeOutput* last_processed_parameter_;
-
   /**
    * @brief Used for thread safety from main thread
    */
@@ -340,6 +322,11 @@ private:
    */
   bool can_be_deleted_;
 
+  /**
+   * @brief Primary node output
+   */
+  NodeOutput* output_;
+
 private slots:
   void InputChanged(rational start, rational end);