made vast improvements to rendering engine and node structure

This was many changes that were largely fundamentally related. They included:
- More const modifiers to enforce read only node graphs
- Support for fragment and vertex shaders from the nodes
- Support for node code loaded externally (embedded into the binary)
- Fixed issue preventing two textures from being used in a shader
- Removed several unused functions and cleaned up code
- Fixed video media node misreading its matrix input

app/node/generator/solid/solid.cpp

@@ -53,7 +53,12 @@ QString SolidGenerator::Description() const
   return tr("Generate a solid color.");
 }
 
-QString SolidGenerator::Code() const
+bool SolidGenerator::IsAccelerated() const
+{
+  return true;
+}
+
+QString SolidGenerator::CodeFragment() const
 {
   return "#version 110\n"
          "\n"