Add a worker

Offload all the asm.js code to a second thread. This is usually the
source of intermittent frontend freezes when running single-threaded.

js/libtextsecure.js

@@ -39483,8 +39483,6 @@ function generateKeys(count, progressCallback) {
         throw new Error('Invalid signedKeyId');
     }
 
-    textsecure.protocol_wrapper.startWorker();
-
     var store = textsecure.storage.axolotl;
     return store.getMyIdentityKey().then(function(identityKey) {
         var result = { preKeys: [], identityKey: identityKey.pubKey };
@@ -39518,7 +39516,6 @@ function generateKeys(count, progressCallback) {
         textsecure.storage.put('maxPreKeyId', startId + count);
         textsecure.storage.put('signedKeyId', signedKeyId + 1);
         return Promise.all(promises).then(function() {
-            textsecure.protocol_wrapper.stopWorker();
             return result;
         });
     });