Fix exit table, set delayed_withdrawn in exits

- In exit table, `instant_withdrawn`, `delayed_withdraw_request`, and
  `delayed_withdrawn` were referencing batch_num.  But these actions happen
  outside a batch, so they should reference a block_num.
- Process delayed withdrawns:
    - In Synchronizer, first match a Rollup delayed withdrawn request, with the
      WDelayer deposit (via TxHash), and store the owner and token associated
      with the delayed withdrawn.
    - In HistoryDB: store the owner and token of a delayed withdrawal request
      in the exit_tree, and set delayed_withdrawn when the withdraw is done in
      the WDelayer.
- Update dependency of sqlx to master
    - Last release of sqlx is from 2018 October, and it doesn't support
      `NamedQuery` with a slice of structs, which is used in this commit.

db/utils.go

@@ -1,7 +1,6 @@
 package db
 
 import (
-	"database/sql"
 	"encoding/base64"
 	"fmt"
 	"math/big"
@@ -180,7 +179,7 @@ func SlicePtrsToSlice(slice interface{}) interface{} {
 }
 
 // Rollback an sql transaction, and log the error if it's not nil
-func Rollback(txn *sql.Tx) {
+func Rollback(txn *sqlx.Tx) {
 	err := txn.Rollback()
 	if err != nil {
 		log.Errorw("Rollback", "err", err)