A variety of logging improvements to track down bugs (#1832)

* Log when we get a blocked numbers sync message

* Save three old signed keys in addition to the current active

* Remove the mystery from all the error-related log messages

* Log successful load of signed key - to help debug prekey errors

* removeSignedPreKey: Don't hang or crash in error cases

* Log on top-level unhandled promise rejection

* Remove trailing comma in param list, Electron 1.6 does not like

* Harden top-level error handler for strange object shapes

libtextsecure/message_receiver.js

@@ -730,6 +730,7 @@ MessageReceiver.prototype.extend({
         }.bind(this));
     },
     handleBlocked: function(envelope, blocked) {
+        console.log('Setting these numbers as blocked:', blocked.numbers);
         textsecure.storage.put('blocked', blocked.numbers);
     },
     isBlocked: function(number) {