[NbtkButton] remove the internal table used to lay out icon and contents
[NbtkButton] remove the internal table used to lay out icon and contents

This prevents the use of an extra actor for layouting and also allows
icons to be used in conjunction with any contents added with the container
api.

pwithnall/mx,jonnylamb/mx,clutter-project/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx,jonnylamb/mx,jonnylamb/mx,clutter-project/mx,clutter-project/mx,pwithnall/mx