Use the updated ledger state in ingest

[bartekn]

This PR fixes random DB constraint errors like (and similar):

import session failed: Ingestion.Flush error: Error adding values while inserting to history_effects: Error adding values while inserting to history_effects: exec failed: pq: duplicate key value violates unique constraint "hist_e_by_order"

The reason is a synchronization issue between App.UpdateLedgerState and ingest.System.runOnce go routines. Both go routines are executed every second by the application ticker. The following sequence of events is possible:

Time	Tick1	Tick2
1	UpdateLedgerState result = [horizon ledger = 10, core ledger = 11]
2	Start ingest session ledgers: [11, 11]
3		UpdateLedgerState result = [horizon ledger = 10, core ledger = 11]
4	Finish ingest session ledgers: [11, 11]
5		Start ingest session ledgers: [11, 11]
6		Error in ingest session ledgers: [11, 11] (because already saved in t=4)

So it is possible that ingest.System.runOnce reads the stale state of ledgers. The simple fix in this PR moves loading the state to ingest.System.runOnce. The long-term fix, in my opinion, should remove synchronization requirement in ingest package (use internal state only, use infinite for instead of ticker etc.).

Close #513.

PS. I've been searching for this for so long! It feels good! 🤓

[robertDurst]

LGTM based on conversation we had and working with tick/latest ledger state in my current horizon PR. However, may want some input from someone more familiar with the ingestion codebase.

[robertDurst]

ingesiton -> ingestion

[bartekn]

Fortunately, I found a possible deadlock and fixed it in 79e453a. Deadlock was possible when one of the DB queries errors (this did not set i.current = nil and making a new ingest sessions impossible). We should really do: #613.