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/readerhighlight.lua

@@ -241,6 +241,7 @@ function ReaderHighlight:onHold(arg, ges)
         end
         UIManager:setDirty(self.dialog, "partial")
         -- TODO: only mark word?
+        -- Unfortunately, CREngine does not return good coordinates
         -- UIManager:setDirty(self.dialog, "partial", self.selected_word.sbox)
     end
     return true
@@ -368,9 +369,7 @@ function ReaderHighlight:onHoldRelease()
             },
             tap_close_callback = function() self:handleEvent(Event:new("Tap")) end,
         }
-        UIManager:show(self.highlight_dialog, nil, nil, function()
-            return "partial", self.highlight_dialog.dimen
-        end)
+        UIManager:show(self.highlight_dialog)
     end
     return true
 end