moving the code (partly) to the renderer and away
from the wxDataViewCtrl class. Adding new in-plae
editors (wxChoice) should be much simpler now.
Also implemented using Validate() before committing
a change to the data model.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45497 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775