section improvements, area elements mostly

app/models/section.rb

@@ -11,6 +11,7 @@ class Section
   has_many :lists
   has_many :orders
   has_many :section_elements
+  has_many :section_areas
 
   attr_protected :supplier_id
 
@@ -99,7 +100,7 @@ class Section
     @for_tables_as_json = h
   end
 
-  def arrange_tables_in_grid
+  def arrange_tables_in_grid(tables = self.tables)
     w = width
     h = height
     n = tables.size