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/readerui.lua

@@ -394,7 +394,7 @@ function ReaderUI:onClose()
         DEBUG("closing document")
         self:onCloseDocument()
     end
-    UIManager:close(self.dialog)
+    UIManager:close(self.dialog, "full")
     -- serialize last used items for later launch
     Cache:serialize()
     running_instance = nil