implemented external xml/shader loading for transitions as well as regular nodes

Transitions are nodes but have a few parameters that are programmatic and always
required. This lets people write external code for transitions as well.

app/node/block/transition/externaltransition.cpp

@@ -0,0 +1,64 @@
+#include "externaltransition.h"
+
+ExternalTransition::ExternalTransition(const QString &xml_meta_filename) :
+  meta_(xml_meta_filename)
+{
+  foreach (NodeInput* input, meta_.inputs()) {
+    AddInput(input);
+  }
+}
+
+Node *ExternalTransition::copy() const
+{
+  return new ExternalTransition(meta_.filename());
+}
+
+QString ExternalTransition::Name() const
+{
+  return meta_.Name();
+}
+
+QString ExternalTransition::id() const
+{
+  return meta_.id();
+}
+
+QString ExternalTransition::Category() const
+{
+  return meta_.Category();
+}
+
+QString ExternalTransition::Description() const
+{
+  return meta_.Description();
+}
+
+void ExternalTransition::Retranslate()
+{
+  meta_.Retranslate();
+}
+
+bool ExternalTransition::IsAccelerated() const
+{
+  return true;
+}
+
+QString ExternalTransition::AcceleratedCodeVertex() const
+{
+  return meta_.vert_code();
+}
+
+QString ExternalTransition::AcceleratedCodeFragment() const
+{
+  return meta_.frag_code();
+}
+
+int ExternalTransition::AcceleratedCodeIterations() const
+{
+  return meta_.iterations();
+}
+
+NodeInput *ExternalTransition::AcceleratedCodeIterativeInput() const
+{
+  return meta_.iteration_input();
+}