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/renderbackend.h

@@ -14,8 +14,6 @@ public:
 
   virtual bool Init() = 0;
 
-  virtual void GenerateFrame(const rational& time) = 0;
-
   virtual void Close() = 0;
 
   const QString& GetError() const;