[apps] create an abstract class for node

Change-Id: I3a946df720c37ec2b087cf6131ea886da3e26c95

apps/node.cpp

@@ -1,9 +1,5 @@
 #include "node.h"
 
-const Node * Node::children(int index) const {
-  return &m_children[index];
-}
-
 int Node::numberOfChildren() {
   return m_numberOfChildren;
 }
@@ -12,10 +8,6 @@ const char * Node::label() const {
   return m_label;
 }
 
-const char * Node::text() const {
-  return m_text;
-}
-
 bool Node::isNull() {
   return (m_label == nullptr);
 }