Add first version of wxBitmapBundle and use it in wxToolBar

This first version provides only a generic implementation of
wxBitmapBundle using a collection of bitmaps and only supports using it
in wxToolBar in wxMSW and wxGTK.

More methods of creating wxBitmapBundle will be provided later and more
functions taking wxBitmap will be changed to take wxBitmapBundle later
too and, of course, all the other ports will be updated to use the new
API too.

build/cmake/files.cmake

@@ -918,6 +918,7 @@ set(GUI_CMN_SRC
     src/generic/creddlgg.cpp
     src/generic/rowheightcache.cpp
     src/generic/animateg.cpp
+    src/common/bmpbndl.cpp
 )
 
 set(GUI_CMN_HDR
@@ -1209,6 +1210,7 @@ set(GUI_CMN_HDR
     wx/creddlg.h
     wx/generic/creddlgg.h
     wx/generic/animate.h
+    wx/bmpbndl.h
 )
 
 set(UNIX_SRC