add f12 shortcut for devtools

fixes minbrowser#1970

Author: PalmerAL

js/defaultKeybindings.js

@@ -1,6 +1,5 @@
 const keybindings = require('keybindings.js')
 var webviews = require('webviews.js')
-var webviewGestures = require('webviewGestures.js')
 var browserUI = require('browserUI.js')
 var focusMode = require('focusMode.js')
 var modalMode = require('modalMode.js')

main/menu.js

@@ -285,6 +285,15 @@ function buildAppMenu (options = {}) {
             sendIPCToWindow(window, 'inspectPage')
           }
         },
+        // this is defined a second time (but hidden) in order to provide two keyboard shortcuts
+        {
+          label: l('appMenuInspectPage'),
+          visible: false,
+          accelerator: 'f12',
+          click: function (item, window) {
+            sendIPCToWindow(window, 'inspectPage')
+          }
+        },
         {
           type: 'separator'
         },