Extend QueryRangeOption with key

[AndreasDegenhart]

Thank you for your work.
Would it still be possible to make changes to the native APi?
If a query with OrderByChild was queried with the same values, the key should also be able to be specified so that the paging works.

https://stackoverflow.com/questions/41788168/how-to-next-and-previous-in-firebase-when-multiple-orderbychild-have-same-value

[manojdcoder]

Sounds like an enhancement.