Support App Groups

[Steven-Chan]

Currently the sdk saves accessToken and currentRecordID in [NSUserDefaults standardUserDefaults], which not accessible across apps in app group, in case I want to add extension to existing app.

[cheungpat]

Steven mentioned that one use case is to support apps with extensions like Watch Extension. The required credentials need to be stored with -[NSUserDefaults initWithSuiteName:].

It seems the app itself cannot find entitled app groups in runtime, therefore some explicit configuration is needed so that the SDK will save credentials in other user defaults object.

[cheungpat]

@Steven-Chan do you want to try implement this?