add menu entry to lookup input word in dictionary

This should close #971.

frontend/apps/reader/modules/readerwikipedia.lua

@@ -11,12 +11,17 @@ local DEBUG = require("dbg")
 local _ = require("gettext")
 
 -- Wikipedia as a special dictionary
-local ReaderWikipedia = ReaderDictionary:new{
+local ReaderWikipedia = ReaderDictionary:extend{
     -- identify itself
     wiki = true,
     no_page = _("No wiki page found."),
 }
 
+-- the super "class" ReaderDictionary has already registers a menu entry
+-- we should override the init function in ReaderWikipedia
+function ReaderWikipedia:init()
+end
+
 function ReaderWikipedia:onLookupWikipedia(word, box)
     -- detect language of the text
     local ok, lang = pcall(Translator.detect, Translator, word)