Add SyncRequest class

Similar in function to an xhr request, a textsecure.SyncRequest object
is initialized from a message sender and receiver pair and initiates a
request for sync from the master device. It later fires a success event
when both contacts and groups are done syncing, or a timeout event after
one minute.

// FREEBIE

js/options.js

@@ -38,10 +38,8 @@
                         var launch = function() {
                             bg.openInbox();
                             bg.removeEventListener('textsecure:contactsync', launch);
-                            clearTimeout(timeout);
                             window.close();
                         };
-                        var timeout = setTimeout(launch, 60000);
                         bg.addEventListener('textsecure:contactsync', launch);
                         view.showSync();
                     }).catch(function(e) {