Much Work

- Definable KeyMaps
- Change 'Tabbable' to just use 'Focusable'

layout_flags.go

@@ -45,6 +45,7 @@ const (
 
 const (
 	LFAlignTopLeft = LayoutFlag(LFAlignHLeft | LFAlignVTop)
+	LFAlignCenter  = LayoutFlag(LFAlignHCenter | LFAlignVCenter)
 )
 
 func (f LayoutFlag) Add(fl LayoutFlag)  { f |= fl }