Move refresh prekeys out of SignalProtocolStore

Use an event/listener instead

// FREEBIE

test/storage_test.js

@@ -91,21 +91,9 @@ describe("SignalProtocolStore", function() {
         });
     });
     describe('removePreKey', function() {
-        var oldGetAccountManager;
         before(function(done) {
-            oldGetAccountManager = window.getAccountManager;
-            window.getAccountManager = function() {
-                return {
-                    refreshPreKeys: function() {
-                        return Promise.resolve();
-                    }
-                };
-            };
             store.storePreKey(2, testKey).then(done);
         });
-        after(function() {
-            window.getAccountManager = oldGetAccountManager;
-        });
         it('deletes prekeys', function(done) {
             store.removePreKey(2, testKey).then(function() {
                 return store.loadPreKey(2).then(function(key) {