nodes: use defined categories rather than arbitrary string based

app/node/block/block.cpp

@@ -63,9 +63,9 @@ Block::Block() :
   set_length_and_media_out(1);
 }
 
-QString Block::Category() const
+QList<Node::CategoryID> Block::Category() const
 {
-  return tr("Block");
+  return {kCategoryTimeline};
 }
 
 const rational &Block::in() const

app/node/block/block.h

@@ -49,7 +49,7 @@ public:
 
   virtual Type type() const = 0;
 
-  virtual QString Category() const override;
+  virtual QList<CategoryID> Category() const override;
 
   const rational& in() const;
   const rational& out() const;

app/node/block/transition/externaltransition.cpp

@@ -50,7 +50,7 @@ QString ExternalTransition::id() const
   return meta_.id();
 }
 
-QString ExternalTransition::Category() const
+QList<Node::CategoryID> ExternalTransition::Category() const
 {
   return meta_.Category();
 }

app/node/block/transition/externaltransition.h

@@ -37,7 +37,7 @@ public:
   virtual QString Name() const override;
   virtual QString ShortName() const override;
   virtual QString id() const override;
-  virtual QString Category() const override;
+  virtual QList<CategoryID> Category() const override;
   virtual QString Description() const override;
 
   virtual void Retranslate() override;