box-layout: add further focus support
box-layout: add further focus support

Convert left/right and up/down into next/previous where appropriate.

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