Add View -> Debug Log to menu bar

Just send an event from the main process to the renderer,
The latter routes it the appropriate view method.

For now it's a no-op unless the main window exists and it is showing the inbox,
which will be addressed in a future commit.

// FREEBIE

app/menu.js

@@ -36,6 +36,12 @@ const template = [
   {
     label: 'View',
     submenu: [
+      {
+        label: 'Debug Log'
+      },
+      {
+        type: 'separator'
+      },
       {
         role: 'reload'
       },