* resource detection is subject to change yet
* don't use UID_2445 for Android <= 4.1
* more useful sync error notification messages
* handle 401 Unauthorized and show account info when notification is tapped
* use VERSION_CODE and buildTime from BuildConfig
* new HTTP User-Agent, VCard PRODID values
* contact sync: store CTag in SyncState
* sync logic: upload contacts, check CTag, multiget