Mgr schedule iterator (#566)

* db based version of PrefixByCumulativeWitnessSize

* db based version of PrefixByCumulativeWitnessSize

* retain all in Trie by default

* fix WitnessLen logic in calcTrie roots

* Rename IntermediateTrieWitnessLenBucket to IntermediateWitnessLenBucket

* handle corner cases in WL

* Use correct incarnation for IH bucket

* use name WitnessSize

* save progress towards db-only witness estimation

* results from trie and from db are still different

* less recursion

* correct incarnation in CumulativeSearch

* reuse results from previous Tick, separate concepts of parent and startKey

* experiment: if not including trie structure to WitnessSize will reduce cumulative error

* tool to generate all IH and tool to calculate assessment of cumulative error

* tool to generate all IH

* Calculate totalWitnessSize based on DB data - then schedule will not overrun state during MGR cycle

* better stats

* Calculate totalWitnessSize based on DB data - then schedule will not overrun state during MGR cycle

* Calculate totalWitnessSize based on DB data - then schedule will not overrun state during MGR cycle

* calculate ticks size distribution

* estimate cumulative error

* fix linter

* resetIH from scratch if needed

* cleanup

* fix test

* fix test