[columns,rows] Remove superfluous widget types, leave containers as Layouts.

rows.lua

@@ -1,10 +1,7 @@
-local BASE = (...):gsub('rows')
+local BASE = (...):gsub('rows', '')
 
 local Layout = require(BASE..'layout')
 
-local Rows = setmetatable({}, Layout)
-Rows.__index = Rows
-
 
 -- Advance position to next row,
 -- given current position, widget dimensions and padding.
@@ -12,8 +9,8 @@ local function rowadvance(x,y, ww,wh, padding)
     return x, y + wh + padding
 end
 
-function Rows.new(args)
-    local self = setmetatable(Layout.new(args), Rows)
+function Rows(args)
+    local self = Layout.new(args)
 
     self.advance = rowadvance
     self.prev = 'up'