added clone functions for nodes

Since nodes are are extremely derivative types, we use a clone/copy function
to produce new types of the derived class easily.

app/node/input/media/audio/audio.cpp

@@ -6,6 +6,11 @@ AudioInput::AudioInput()
   AddParameter(samples_output_);
 }
 
+Node *AudioInput::copy()
+{
+  return new AudioInput();
+}
+
 QString AudioInput::Name()
 {
   return tr("Audio Input");

app/node/input/media/audio/audio.h

@@ -8,6 +8,8 @@ class AudioInput : public MediaInput
 public:
   AudioInput();
 
+  virtual Node* copy() override;
+
   virtual QString Name() override;
   virtual QString id() override;
   virtual QString Category() override;

app/node/input/media/video/video.cpp

@@ -18,6 +18,11 @@ VideoInput::VideoInput()
   AddParameter(texture_output_);
 }
 
+Node *VideoInput::copy()
+{
+  return new VideoInput();
+}
+
 QString VideoInput::Name()
 {
   return tr("Video Input");

app/node/input/media/video/video.h

@@ -11,6 +11,8 @@ class VideoInput : public MediaInput
 public:
   VideoInput();
 
+  virtual Node* copy() override;
+
   virtual QString Name() override;
   virtual QString id() override;
   virtual QString Category() override;