Added quorum_lookup

quorum_lookup picks lookup_result_enties by following rules:
1. If there are quorum lookup_result_enties with the same
timestamp, they are the final result
2. Otherwise the final result is lookup_result_enties with
the greatest timestamp
What does it do? Why is it needed?
Please write a bit more details docs, in particular not what it does, but what is the logic behind decision to implement particular this code