Move helper classes below Firebase in Firebase.h
Move helper classes below Firebase in Firebase.h

ed7coyne/firebase-arduino,FirebaseExtended/firebase-arduino,FirebaseExtended/firebase-arduino,aliafshar/firebase-arduino,aliafshar/firebase-arduino,gguuss/firebase-arduino,aliafshar/firebase-arduino,gguuss/firebase-arduino,FirebaseExtended/firebase-arduino,gguuss/firebase-arduino,proppy/firebase-arduino