[UX] Gesture manager: add action - toggle wifi

As suggested by @poire-z.

koreader#4727 (comment)

I wanted to make the gesture a `W`, but that's a bit too unwieldy. Instead there's the suggestion of a (backward) `W`.

frontend/apps/reader/modules/readergesture.lua

@@ -58,6 +58,7 @@ local action_strings = {
     toggle_gsensor = _("Toggle accelerometer"),
     toggle_rotation = _("Toggle rotation"),
     toggle_reflow = _("Toggle reflow"),
+    toggle_wifi = _("Toggle wifi"),
 
     zoom_contentwidth = _("Zoom to fit content width"),
     zoom_contentheight = _("Zoom to fit content height"),
@@ -118,6 +119,7 @@ local default_multiswipes = {
     "northeast southeast",
     -- "southwest northwest", -- visually ambiguous
     -- "northwest southwest", -- visually ambiguous
+    "northwest southwest northwest",
 }
 local multiswipes = {}
 local multiswipes_info_text = _([[
@@ -155,6 +157,7 @@ function ReaderGesture:init()
         multiswipe_south_east_north_south = self.ges_mode == "gesture_reader" and "zoom_pageheight" or "nothing",
         multiswipe_east_south_west_north = "full_refresh",
         multiswipe_southeast_northeast = self.ges_mode == "gesture_reader" and "follow_nearest_link" or "nothing",
+        multiswipe_northwest_southwest_northwest = Device:hasWifiToggle() and "toggle_wifi",
     }
     local gm = G_reader_settings:readSetting(self.ges_mode)
     if gm == nil then G_reader_settings:saveSetting(self.ges_mode, {}) end
@@ -330,6 +333,7 @@ function ReaderGesture:buildMenu(ges, default)
         {"toggle_gsensor", Device:canToggleGSensor()},
         {"toggle_rotation", not self.is_docless, true},
         {"toggle_reflow", not self.is_docless, true},
+        {"toggle_wifi", Device:hasWifiToggle() and "toggle_wifi", true},
 
         {"zoom_contentwidth", not self.is_docless},
         {"zoom_contentheight", not self.is_docless},
@@ -697,6 +701,20 @@ function ReaderGesture:gestureAction(action, ges)
         else
             self.ui:handleEvent(Event:new("SetScreenMode", "portrait"))
         end
+    elseif action == "toggle_wifi" then
+        local NetworkMgr = require("ui/network/manager")
+
+        if not NetworkMgr:isOnline() then
+            -- NB Normal widgets should use NetworkMgr:promptWifiOn()
+            -- This is specifically the toggle wifi action, so consent is implied.
+            NetworkMgr:turnOnWifi()
+        else
+            NetworkMgr:turnOffWifi()
+
+            UIManager:show(InfoMessage:new{
+                text = _("Wifi disabled."),
+            })
+        end
     elseif action == "suspend" then
         UIManager:suspend()
     elseif action == "exit" then