Add new options to screensaver (#3535)

* Prevent open screensaver more than one in the same time

* Add option to enable/disable background in message screensaver

* fallback to random images if this book cover is excluded feature + fix Disabled (leave screen/page as it is)

* Autostretch disable by default, more fallback options, leave screen as it is

frontend/ui/widget/button.lua

@@ -210,7 +210,9 @@ function Button:onTapSelectButton()
     elseif type(self.tap_input_func) == "function" then
         self:onInput(self.tap_input_func())
     end
-    return true
+    if self.readonly ~= true then
+        return true
+    end
 end
 
 function Button:onHoldSelectButton()