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/block/block.h

@@ -41,8 +41,6 @@ public:
     kEnd
   };
 
-  virtual Block* copy() = 0;
-
   virtual Type type() = 0;
 
   virtual QString Category() override;

app/node/block/clip/clip.cpp

@@ -27,7 +27,7 @@ ClipBlock::ClipBlock()
   AddParameter(texture_input_);
 }
 
-Block *ClipBlock::copy()
+Node *ClipBlock::copy()
 {
   ClipBlock* c = new ClipBlock();
 

app/node/block/clip/clip.h

@@ -32,7 +32,7 @@ class ClipBlock : public Block
 public:
   ClipBlock();
 
-  virtual Block* copy() override;
+  virtual Node* copy() override;
 
   virtual Type type() override;
 

app/node/block/gap/gap.cpp

@@ -24,7 +24,7 @@ GapBlock::GapBlock()
 {
 }
 
-Block *GapBlock::copy()
+Node *GapBlock::copy()
 {
   GapBlock* c = new GapBlock();
 

app/node/block/gap/gap.h

@@ -32,7 +32,7 @@ class GapBlock : public Block
 public:
   GapBlock();
 
-  virtual Block * copy() override;
+  virtual Node * copy() override;
 
   virtual Type type() override;