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    - In Synchronizer, first match a Rollup delayed withdrawn request, with the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      with the delayed withdrawn.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.

api/api_test.go

@@ -222,7 +222,7 @@ func TestMain(m *testing.M) {
 	// Gen exits and add them to DB
 	const totalExits = 40
 	// TODO: UPDATE with til
-	exits := test.GenExitTree(totalExits, batches, accs)
+	exits := test.GenExitTree(totalExits, batches, accs, blocks)
 	err = api.h.AddExitTree(exits)
 	if err != nil {
 		panic(err)