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

js/background.js

@@ -78,6 +78,9 @@
             appView.openInstaller();
         }
 
+        Whisper.events.on('showDebugLog', function() {
+            appView.inboxView.showDebugLog();
+        });
         Whisper.events.on('unauthorized', function() {
             appView.inboxView.networkStatusView.update();
         });