intelligent event listeners

[Orlandster]

Till now each time an event fires the whole query gets executed. Since Firebase returns the push key of the modified child, we are able to simply add / update or reomve this child.

e.g. active query

result = [entry1: { name: "john" }, entry2: { name: "misterX" }]

entry3 gets added -> get value (already in event callback) -> run through query -> push to array
entry2 gets updated -> get value - run through query -> add, remove or delete it in array
entry2 gets deleted -> get key -> delete it from array

This implementation should be very easy. Probably there should also be some kind of queue to avoid conflicts.