Added callback to Weave.Service.onStartup, which the Fennec UI uses to notify user that Weave has connected, that it ran into an error, or that it's awaiting configuration. Started moving fennec preferences from HTML to XUL.

services/sync/modules/service.js

@@ -313,8 +313,8 @@ WeaveSvc.prototype = {
       } catch (e) {}
     self.done();
   },
-  onStartup: function WeaveSvc_onStartup() {
-    this._onStartup.async(this);
+  onStartup: function WeaveSvc_onStartup(callback) {
+    this._onStartup.async(this, callback);
   },
 
   _initLogs: function WeaveSvc__initLogs() {