Better device id without privacy issue

[xcv58]

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[xcv58]

According to http://android-developers.blogspot.com/2011/03/identifying-app-installations.html

The ANDROID_ID may be the best choice.

From http://android-developers.blogspot.com/2015/05/a-closer-look-at-google-play-services-75.html
Instance ID seems better because it ties each app.

But here we got a new issue. If two apps use Maybe Library in one phone. The Instance ID may override each other.

Probably a better way is put gcmid to device->package->gcmid instead of current implementation: device->gcmid.

That means: in backend, we have deviceid means a real Android device or a profile on Android deivce.
That deviceid may have multiple gcmid.

[xcv58]

According to https://developers.google.com/instance-id/reference/

The Instance ID API lets you integrate Instance ID with your Android or iOS app. Instance ID provides a unique identifier for each instance of your app and a mechanism to authenticate and authorize actions, like sending messages via Google Cloud Message (GCM). The InstanceID is long lived, but may expire for the following reasons: