many graphics performance tweaks

* use hardware vertex buffers (video memory)
* cache text drawing with vertex buffers instead of framebuffers
* avoid recalculating texture transformation matrix

src/framework/graphics/paintershaderprogram.h

@@ -54,7 +54,7 @@ public:
     void setOpacity(float opacity);
     void setTexture(const TexturePtr& texture);
     void setUniformTexture(int location, const TexturePtr& texture, int index);
-    void draw(const CoordsBuffer& coordsBuffer, DrawMode drawMode = Triangles);
+    void draw(CoordsBuffer& coordsBuffer, DrawMode drawMode = Triangles);
 
 private:
     DrawMode m_drawMode;