Update Synchronizer (node) implementation

- node:
    - Extend config to add initial variables of the smart contracts used as
      defaults before they are changed via events.
    - In stopped channels, set size 1 so that panics are not witheld until the
      node stops completely.
- common:
    - In Smart Contract variables, comment:
      - `WDelayerVariables.HermezRollupAddress` because it's not needed.
      - `RollupVariables.Buckets` because there are no events for it, and for
        now it's not used.
- historydb:
    - Add functions to get and set smart contract variables.
- db:
    - Add `Rollback` function in `utils.go` to reduce boilerplate in sql
      transaction rollbacks in defers in db functions.
    - Update `rollup_vars` and `auction_vars` (renamed from `consensus_vars`)
      table, and add `wdelayer_vars` table.
- synchronizer:
    - Synchronize WDelayer
    - Handle SC variables properly
- test/ethclient:
    - Add essential implementation of WDelayer

db/utils.go

@@ -1,6 +1,7 @@
 package db
 
 import (
+	"database/sql"
 	"encoding/base64"
 	"fmt"
 	"math/big"
@@ -192,3 +193,11 @@ type Paginationer interface {
 	GetPagination() *Pagination
 	Len() int
 }
+
+// Rollback an sql transaction, and log the error if it's not nil
+func Rollback(txn *sql.Tx) {
+	err := txn.Rollback()
+	if err != nil {
+		log.Errorw("Rollback", "err", err)
+	}
+}