DWT extensions

[Frank Benoit]

All SWT widgets have the possibility to set and get a data values that
are passed as Objects. DWT extends those for Strings explicitly and adds:
 public void setDataStr( String value );
 public void setDataStr( String key, String value );
 public String getDataStr();
 public String getDataStr( String value );

For Listener and Runnable there are already the template function
dgListener and dgRunnable. Now there is also support for that in
 - SelectionListener
 - CTabFolderListener
 - CTabFolder2Listener