Add account_update SQL table with balances and nonces

config/config.go

@@ -232,6 +232,11 @@ type Node struct {
 		// `Eth.LastBatch`).  This value only affects the reported % of
 		// synchronization of blocks and batches, nothing else.
 		StatsRefreshPeriod Duration `validate:"required"`
+		// StoreAccountUpdates when set to true makes the synchronizer
+		// store every account update in the account_update SQL table.
+		// This allows querying nonces and balances from the HistoryDB
+		// via SQL.
+		StoreAccountUpdates bool
 	} `validate:"required"`
 	SmartContracts struct {
 		// Rollup is the address of the Hermez.sol smart contract