BAASBoxAuthenticator support

[BAASBoxAuthenticator](https://github.com/spomytkin/BAASBoxAuthenticator) implementation of  [customtAccountAuthenticator](http://developer.android.com/reference/android/accounts/AbstractAccountAuthenticator.html) requires access token to be returned on [getAuthToken](http://developer.android.com/reference/android/accounts/AbstractAccountAuthenticator.html#getAuthToken%28android.accounts.AccountAuthenticatorResponse,%20android.accounts.Account,%20java.lang.String,%20android.os.Bundle%29) 
and  [addAccount](http://developer.android.com/reference/android/accounts/AbstractAccountAuthenticator.html#addAccount%28android.accounts.AccountAuthenticatorResponse,%20java.lang.String,%20java.lang.String,%20java.lang.String[],%20android.os.Bundle%29)