clean up refreshes

This is a larger clean-up of the refresh situation.
The general shift is that refreshes are now mainly triggered by
the (top-level) widgets when they get shown or closed via UIManager.

All refreshes for the widgets when they are in use were handled by
themselves before. This adds the case of showing/closing.

It is the desired result of not having UIManager:show()/:close()
do (full screen) refreshes on its own.

frontend/apps/reader/modules/readerdictionary.lua

@@ -106,7 +106,7 @@ function ReaderDictionary:showDict(word, results, box)
             -- differentiate between dict and wiki
             wiki = self.wiki,
         }
-        UIManager:show(self.dict_window, nil, nil, "none")
+        UIManager:show(self.dict_window)
     end
 end