ReaderUI: Properly neuter gesture handling from InputContainer modules

None[1] of them actually rely on their own onGesture handler, they
all register their own stuff to ReaderUI's.
Hotfix #9710 revealed that the way this was handled didn't exactly
work as expected ;).

The only thing that consumes ges_events is InputContainer's onGesture
method. All these modules *extend* InputContainer, but none of them
*implement* a custom onGesture, so self.onGesture = nil was just a NOP,
they always access InputContainer's method via inheritance.
If we actively want to neuter it, we *have* to implement it in that
module (with a NOP).

[1] The exception being ReaderZooming, but that only when in flip mode.

frontend/apps/reader/modules/readerpaging.lua

@@ -118,16 +118,18 @@ function ReaderPaging:init()
     end
     self.pan_interval = time.s(1 / self.pan_rate)
     self.number_of_pages = self.ui.document.info.number_of_pages
+
+    -- delegate gesture listener to readerui, NOP our own
+    self.ges_events = nil
 end
 
+function ReaderPaging:onGesture() end
+
 function ReaderPaging:onReaderReady()
     self:setupTouchZones()
 end
 
 function ReaderPaging:setupTouchZones()
-    -- delegate gesture listener to readerui
-    self.ges_events = {}
-    self.onGesture = nil
     if not Device:isTouchDevice() then return end
 
     local forward_zone, backward_zone = self.view:getTapZones()