Make wxAnimationImpl private and get rid of wxAnimationImplType

Simplify and streamline animation classes relationship: wxAnimation is
the only public class representing an animation and it can be created by
both the native wxAnimationCtrl and wxGenericAnimationCtrl using the new
public CreateAnimation() method.

Replace wxAnimationImplType enum with more flexible type info based
check.

include/wx/generic/animate.h

@@ -92,9 +92,8 @@ public:     // extended API specific to this implementation of wxAnimateCtrl
     wxBitmap& GetBackingStore()
         { return m_backingStore; }
 
-    static wxAnimationImpl* CreateAnimationImpl(wxAnimationImplType implType);
-
 protected:      // internal utilities
+    virtual wxAnimationImpl* DoCreateAnimationImpl() const wxOVERRIDE;
 
     // resize this control to fit m_animation
     void FitToAnimation();