move configurable to Document class

since every document type is depend on it now

frontend/document/djvudocument.lua

@@ -10,7 +10,6 @@ DjvuDocument = Document:new{
 	djvulibre_cache_size = nil,
 	dc_null = DrawContext.new(),
 	options = KoptOptions,
-	configurable = Configurable,
 	koptinterface = KoptInterface,
 }