separation of previous renderer into base and derivation complete

The previous iteration was fairly OpenGL-heavy. It's now been separated into
a base class that is OpenGL independent and a derived class that is
OpenGL-based. Over time this should allow for portability away from OpenGL
if necessary.

app/render/backend/opengl/openglframebuffer.h

@@ -42,9 +42,9 @@ public:
 
   void Release();
 
-  void Attach(RenderTexturePtr texture);
+  void Attach(OpenGLTexturePtr texture);
 
-  void AttachBackBuffer(RenderTexturePtr texture);
+  void AttachBackBuffer(OpenGLTexturePtr texture);
 
   void Detach();
 
@@ -60,7 +60,7 @@ private:
 
   GLuint buffer_;
 
-  RenderTexturePtr texture_;
+  OpenGLTexturePtr texture_;
 };
 
 #endif // OPENGLFRAMEBUFFER_H