Better handling of network disconnection/reconnection (#1546)

* Ensure that our preload.js setImmediate call finds right function

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* Our own socket close event, better logging, unregistration

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* Return CLOSED for NetworkStatusView if we've fully disconnected

* background.js: Remove messageReceiver = null, log in connect()

A null messageReciever makes the NetworkStatusView think we're online.

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preload.js

@@ -41,7 +41,7 @@
 
   // Linux seems to periodically let the event loop stop, so this is a global workaround
   setInterval(function() {
-    setImmediate(function() {});
+    window.nodeSetImmediate(function() {});
   }, 1000);
 
   window.EmojiConvertor = require('emoji-js');