Support content title with gcm notifications on android

In Android you can set a custom title in Android: http://developer.android.com/guide/topics/ui/notifiers/notifications.html with setContentTitle(),
the Android version of the push plugin should support that too

Currently it uses the app name:
https://github.com/aerogear/aerogear-pushplugin-cordova/blob/master/src/android/org/jboss/aerogear/cordova/push/NotificationMessageHandler.java#L73

But it would be nice if the 'title' value of the received push message would be used:

.setContentTitle(extras.getString("title"))

If the title is NOT present, showing the app name makes sense