Upgrade 2 messages every 30 seconds

This results in 4 messages per minute or 240 messages per hour.

js/background.js

@@ -79,16 +79,17 @@
 
   /* eslint-enable */
   /* jshint ignore:start */
+  const NUM_MESSAGE_UPGRADES_PER_IDLE = 2;
   const idleDetector = new IdleDetector();
   idleDetector.on('idle', async () => {
     const results = await MessageDataMigrator.processNext({
       BackboneMessage: Whisper.Message,
       BackboneMessageCollection: Whisper.MessageCollection,
-      count: 3,
+      count: NUM_MESSAGE_UPGRADES_PER_IDLE,
       upgradeMessageSchema,
       wrapDeferred,
     });
-    console.log('Message schema upgrade:', results);
+    console.log('Upgrade message schema:', results);
 
     if (!results.hasMore) {
       idleDetector.stop();

js/modules/idle_detector.js

@@ -3,7 +3,7 @@
 const EventEmitter = require('events');
 
 
-const POLL_INTERVAL_MS = 10 * 1000;
+const POLL_INTERVAL_MS = 30 * 1000;
 const IDLE_THRESHOLD_MS = 25;
 
 class IdleDetector extends EventEmitter {