Changes to Canvas class according to review:

- renamed CCanvas -> Canvas.cpp
- replaced shared_ptr<Canvas> with Canvas&
- removed getSurface method

client/battle/BattleEffectsController.h

@@ -21,7 +21,7 @@ VCMI_LIB_NAMESPACE_END
 
 struct SDL_Surface;
 class CAnimation;
-class CCanvas;
+class Canvas;
 class BattleInterface;
 class BattleRenderer;
 class CPointEffectAnimation;