Dictionary and wikipedia enhancements (#2393)

Stardict:
- remove duplicate results
- better cleaning of selection
- append results from a 2nd query of a 2nd set of dictionaries
  in data/dict_ext/

Wikipedia:
- use the search API for better results
- allow viewing the full page content of a result in a bigger window
- allow queries for multiple languages
- available languages can be set in settings.reader.lua :
    ["wikipedia_languages"] = {"en", "fr", "it"}
- "Wikipedia lookup" added to Tools menu

For both:
- allow selection of multiple words for a new lookup (so one can
  actually browse wikipedia)
- allow continuous reading with Tap
- display "current result / total number of results"

Details in #2393

frontend/apps/reader/modules/readerhighlight.lua

@@ -494,8 +494,7 @@ function ReaderHighlight:onHighlightDictLookup()
     DEBUG("dictionary lookup highlight")
     self:highlightFromHoldPos()
     if self.selected_text then
-        local text = require("util").stripePunctuations(self.selected_text.text)
-        self.ui:handleEvent(Event:new("LookupWord", text))
+        self.ui:handleEvent(Event:new("LookupWord", self.selected_text.text))
     end
 end