Add addToLayout()-method to KitConfigWidget.

Provide default implementation to do a single-line layout
and let the DebuggerKitConfigWidget span 3 rows, aligning label
and button accordingly.

Change-Id: I0fb3a3116a593822da9c4499c142b8a8255c02d0
Reviewed-by: Eike Ziller <eike.ziller@nokia.com>
Reviewed-by: hjk <qthjk@ovi.com>