Adds "Better rendering of list items" to Style tweaks (#3968)

Alternate rendering of list items as block elements (instead of
inline/final).
Check the built DOM is still coherent with styles on stylesheet
change, and propose to reload the document if not. Also
invalidate cache on close in that case so a new DOM is built
at next opening.
ReaderStyleTweak: fix tweak css duplication; when globally
enabled, when disabling and re-enabling locally, the css would
be added twice to the final CSS.
Also adds !important to "sub_sup_smaller" tweak, and increase
its priority so it can override "font_size_all_inherit".
Adds CreDocument:getCacheFilePath() for futur features.

frontend/apps/reader/modules/readermenu.lua

@@ -274,9 +274,11 @@ function ReaderMenu:onShowReaderMenu(tab_index)
 end
 
 function ReaderMenu:onCloseReaderMenu()
-    self.last_tab_index = self.menu_container[1].last_index
-    self:onSaveSettings()
-    UIManager:close(self.menu_container)
+    if self.menu_container then
+        self.last_tab_index = self.menu_container[1].last_index
+        self:onSaveSettings()
+        UIManager:close(self.menu_container)
+    end
     return true
 end