Generate key events in generic wxDataViewCtrl implementation.

Forward wxEVT_CHAR events from wxDataViewMainWindow to the parent window so
that they could be processed at wxDataViewCtrl level.

Call DisableKeyboardScrolling() to ensure that cursor movement keys are not
always eaten by the parent window but can be used for the navigation in the
control if they're not processed by user.

Add a test keyboard handler to the dataview sample to check that handling keys
in wxDataViewCtrl does work.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64957 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775